How to fix error irql-not-less-or-equal in Horizon Forbidden West

Solution Steps

1. 1 Run Horizon Forbidden West as Administrator. Navigate to the game folder, right-click the .exe → Properties → Compatibility → check 'Run this program as an administrator' → Apply. This gives Horizon Forbidden West full system access and fixes permission-related crashes.
2. 2 Update Windows to the latest version. Settings → Windows Update → Check for updates. Install ALL updates, especially 'Optional' driver updates. Horizon Forbidden West requires the latest Windows components for stability.
3. 3 Disable fullscreen optimizations. Right-click Horizon Forbidden West.exe → Properties → Compatibility → check 'Disable fullscreen optimizations' → Apply. This prevents Windows from interfering with the game's rendering pipeline.
4. 4 Install Horizon Forbidden West on an SSD if it's currently on an HDD. Slow disk reads during gameplay cause asset streaming stutters that can cascade into crashes. An SSD eliminates this bottleneck.
5. 5 Check your RAM stability. Press Windows key + R, type 'mdsched.exe' and press Enter → Restart now. Faulty RAM causes random crashes in Horizon Forbidden West that are impossible to reproduce consistently.
6. 6 Temporarily disable your antivirus real-time protection and test Horizon Forbidden West. Add the game folder to antivirus exclusions. Security software sometimes quarantines game files or blocks their execution.
7. 7 Lower Horizon Forbidden West graphics settings temporarily. Set everything to Low/Off, disable Ray Tracing, disable DLSS/FSR. If crashes stop, increase settings one by one until you find the problematic setting — usually shadows, textures, or ray tracing.
8. 8 If Horizon Forbidden West still crashes: uninstall the game, delete all remaining folders in SteamApps\common and %LOCALAPPDATA%, restart your PC, reinstall. This clean slate approach fixes stubborn corruption that verification misses.