How to Fix System Thread Exception Not Handled Error in Windows (2026 Guide)

If your Windows PC crashes with a blue screen showing SYSTEM_THREAD_EXCEPTION_NOT_HANDLED, you are dealing with one of the most common but fixable BSoD (Blue Screen of Death) errors. The good news: this error almost always points to a specific driver or system file conflict, and once you know where to look, you can resolve it without reinstalling Windows.

This guide walks you through every meaningful fix, in order of how likely each one is to work.

What Does System Thread Exception Not Handled Actually Mean?

The error name tells you most of what you need to know. A “system thread” is a background process running inside the Windows kernel. When that thread encounters an exception it cannot handle (such as an instruction it does not recognize or a memory access violation), Windows stops everything and throws the blue screen rather than risk corrupting your data.

The stop code is usually accompanied by a filename in parentheses, like:

• SYSTEM_THREAD_EXCEPTION_NOT_HANDLED (nvlddmkm.sys) — NVIDIA graphics driver
• SYSTEM_THREAD_EXCEPTION_NOT_HANDLED (atikmdag.sys) — AMD graphics driver
• SYSTEM_THREAD_EXCEPTION_NOT_HANDLED (ntfs.sys) — File system driver
• SYSTEM_THREAD_EXCEPTION_NOT_HANDLED (dxgmms2.sys) — DirectX graphics kernel

The filename is your biggest clue. Write it down or photograph the screen before rebooting.

Common Causes at a Glance

Cause	How Common	Typical Fix
Outdated or corrupt graphics driver	Very common	Update or roll back driver
Recently installed driver conflicts	Common	Uninstall new driver
Corrupt Windows system files	Moderate	Run SFC and DISM
Faulty RAM	Less common	Run memory diagnostics
Incompatible hardware after update	Moderate	Roll back Windows update
Hard drive errors	Less common	Run CHKDSK
Overclocking instability	Rare	Reset BIOS to defaults

Step 1: Note the Filename in the Error Message

Before you do anything else, identify the driver file named in the error. It appears below the stop code on the blue screen, enclosed in parentheses.

If you missed it and your PC keeps crashing at boot, start Windows in Safe Mode. Safe Mode loads only essential drivers, which usually prevents the crash and gives you access to fix the problem.

To boot into Safe Mode:

1. Hold Shift and click Restart from the Windows login screen or Start menu
2. Go to Troubleshoot > Advanced Options > Startup Settings
3. Press F4 for Safe Mode or F5 for Safe Mode with Networking

Once inside Safe Mode, continue with the steps below.

Step 2: Update or Roll Back the Problem Driver

Graphics drivers cause this error more than anything else. Whether the file named is nvlddmkm.sys, atikmdag.sys, dxgmms2.sys, or something similar, the fix involves your GPU driver.

If the crash started after a driver update, roll it back:

1. Right-click Start and open Device Manager
2. Expand Display Adapters
3. Right-click your GPU and select Properties
4. Go to the Driver tab and click Roll Back Driver
5. Restart your PC

If the driver is outdated, update it properly:

Do not rely on Windows Update for GPU drivers. Go directly to the manufacturer:

• NVIDIA drivers: nvidia.com/Download/index.aspx
• AMD drivers: amd.com/en/support

For a clean installation, use Display Driver Uninstaller (DDU) in Safe Mode to fully remove the old driver before installing the new one. This prevents leftover registry entries from causing continued instability.

Step 3: Run System File Checker and DISM

If the problem driver is a Windows system file like ntfs.sys or storport.sys, your best tool is the built-in SFC scanner. It checks every protected system file and replaces corrupted ones from a local cache.

Open Command Prompt as Administrator and run:

sfc /scannow

Wait for the scan to complete. This takes 10 to 20 minutes. If it finds and fixes issues, restart and test.

If SFC reports that it found corrupt files it could not fix, run DISM to repair the Windows image itself:

DISM /Online /Cleanup-Image /RestoreHealth

This tool connects to Windows Update servers to pull fresh copies of corrupted components. After it finishes, run sfc /scannow again and restart.

Step 4: Check Windows Event Viewer for Details

Event Viewer logs what happened right before the crash, which helps you pinpoint the exact driver or application at fault.

1. Press Windows + X and open Event Viewer
2. In the left panel, go to Windows Logs > System
3. Look for entries with a red “Error” icon timestamped around the time of your crash
4. Double-click an entry to read the full description

The log will often mention a specific driver name, service, or executable. This gives you a concrete target to investigate.

Step 5: Analyze the Minidump File

Every BSoD creates a small crash log called a minidump. Analyzing it tells you the exact driver that caused the crash, even if the blue screen disappeared too fast to read.

Location of minidump files:

C:\Windows\Minidump\

To analyze these files, download WinDbg from the Microsoft Store or use the free tool WhoCrashed. WhoCrashed is simpler for non-technical users and generates a plain-English report that names the responsible driver.

According to Microsoft’s official debugging documentation, minidump analysis is the most reliable method for identifying the root cause of stop errors.

Step 6: Uninstall Recently Installed Software or Drivers

Think about what changed on your system right before the crashes started:

• Did you install a new program?
• Did Windows Update run?
• Did you connect new hardware?
• Did you update any driver manually?

To uninstall a program:

Go to Settings > Apps > Installed Apps, find the software, and remove it.

To uninstall a problematic Windows Update:

1. Go to Settings > Windows Update > Update History
2. Click Uninstall Updates
3. Find the most recent update, right-click, and uninstall

Restart after each removal and check if the crashes stop.

Step 7: Test Your RAM

Faulty RAM causes a wide range of BSoD errors, including this one. Windows has a built-in memory diagnostic tool.

1. Press Windows + R, type mdsched.exe, and press Enter
2. Choose Restart now and check for problems
3. Windows will reboot and run the test automatically

If errors appear, reseat your RAM sticks (remove them and firmly push them back in). If errors persist, the RAM may need to be replaced. Test one stick at a time if you have multiple sticks to identify which one is faulty.

For more thorough testing, use MemTest86, which runs outside of Windows and catches errors the Windows tool sometimes misses.

Step 8: Run CHKDSK for Drive Errors

A failing hard drive or SSD can cause system file corruption that triggers this error. Run a disk check on your Windows drive.

Open Command Prompt as Administrator and type:

chkdsk C: /f /r

The /f flag fixes errors, and /r locates bad sectors and recovers data. You will be asked to schedule the scan for the next restart since Windows cannot check the active system drive while it is running. Type Y and restart.

The scan can take anywhere from 20 minutes to a couple of hours depending on drive size and health.

Step 9: Reset or Reinstall Windows as a Last Resort

If nothing above has worked, the problem may be deeply embedded in your Windows installation. In that case, a reset is faster and less frustrating than continued troubleshooting.

To reset Windows while keeping your files:

1. Go to Settings > System > Recovery
2. Click Reset this PC
3. Choose Keep my files
4. Follow the prompts

This reinstalls Windows without deleting your personal files, but it does remove all installed applications. If even a fresh reset does not stop the crashes, the issue is likely hardware, specifically the RAM, drive, or (less commonly) the motherboard.

Preventing This Error in the Future

Habit	Why It Helps
Keep GPU drivers updated through manufacturer sites	Avoids compatibility gaps between driver and Windows
Delay major Windows Updates by 1 to 2 weeks	Lets Microsoft patch issues others encounter first
Do not overclock without proper cooling	Instability from heat causes random BSoDs
Run SFC monthly if you install lots of software	Catches corruption before it causes crashes
Keep at least 15% free space on your system drive	Low disk space degrades driver and system performance

Quick Reference: Which Fix Matches Which File

File Named in Error	Most Likely Cause	First Action
nvlddmkm.sys	NVIDIA driver	Update or reinstall NVIDIA driver
atikmdag.sys / amdkmdag.sys	AMD driver	Update or reinstall AMD driver
dxgmms2.sys	DirectX / GPU scheduling	Update GPU driver, disable hardware GPU scheduling
ntfs.sys	NTFS file system	Run SFC, then CHKDSK
storport.sys	Storage controller	Update storage drivers, check drive health
usbxhci.sys	USB controller	Unplug USB devices, update chipset drivers
No filename shown	Unknown driver	Use WhoCrashed to analyze minidump

Conclusion

The System Thread Exception Not Handled error in Windows is almost always caused by a driver problem, and most of the time it is the graphics driver. Start by identifying the filename in the error, boot into Safe Mode if needed, and either update or roll back the driver in question.

If that does not solve it, run SFC and DISM, test your RAM, and check your drive with CHKDSK. For persistent cases, Event Viewer and minidump analysis from a tool like WhoCrashed will tell you exactly what is causing the crash.

Work through the steps in order, restart between each one, and you will almost certainly resolve this without a full reinstall.