Installer blocked by SmartScreen or antivirus

Verify the download source (download.osgeo.org). Temporarily allow the installer, run as Administrator, or whitelist the file in your AV. Avoid disabling AV permanently.

Missing DLLs or Python errors on startup

This often means mixed installers or missing dependencies. Uninstall conflicting QGIS installs, reinstall via OSGeo4W, and ensure you choose the correct architecture (64-bit).

QGIS crashes on startup after update

Try launching QGIS with a clean profile (rename the QGIS profile folder), check plugin compatibility, and reinstall if needed. Backup projects before actions.

Troubleshooting hub

Fix Common QGIS Install Errors on Windows

Solutions for installer blocks, missing dependencies, crashes, and common startup issues. Safe official download via OSGeo4W is linked below.

Download OSGeo4W Back to Install Guide

Safety first: verify the download URL (download.osgeo.org). Backup projects before major changes.

Common categories

Installer blocked / SmartScreen
Missing DLLs / Python issues
Startup crashes / slow rendering
Plugin conflicts / broken profiles

Step‑by‑step fixes

Installer blocked (SmartScreen/AV)

Verify the file and allow if flagged: right‑click → Properties → check Origin, then Run as Administrator. If your AV blocks it, temporarily whitelist the installer or use an admin account. Never run unknown executables.

Missing DLLs or "ImportError"

Often caused by mixed installers or Python environment conflicts. Uninstall other QGIS installs, remove leftover OSGeo folders, then reinstall via OSGeo4W (choose correct architecture).

QGIS crashes on start

Start with a clean profile: rename the QGIS profile folder (in %APPDATA%/QGIS/QGIS3/profiles). If it starts, a plugin or setting caused the crash—disable plugins and reintroduce settings one by one.

Slow rendering / memory errors

Use fewer visible layers, enable scale‑based rendering, store data on SSD, and increase RAM. For large rasters, use overviews and efficient formats like GeoPackage.

Broken plugins after update

Plugins may target a specific API. Disable plugins, update them, or revert to LTR if plugins are incompatible. Reinstall problematic plugins from the official repository.

Clean uninstall

Uninstall QGIS via Apps & Features, then remove C:\\OSGeo4W (or MSI install folder) and %APPDATA%/QGIS if you want a full reset. Backup projects before deleting.

Quick commands & checks

Check architecture: In Windows Settings → System → About, make sure you run 64‑bit if you downloaded 64‑bit installer.

Run as Admin: Right‑click the installer → Run as administrator.

Verify source: The official installer is at https://download.osgeo.org/osgeo4w/v2/osgeo4w-setup.exe.

FAQ

SmartScreen warns "Unknown publisher" — is it safe?

SmartScreen may flag unsigned installers. Confirm the source (download.osgeo.org). If confirmed, proceed or temporarily allow via the SmartScreen dialog. Keep AV enabled.

I see Python errors after install. What now?

Python in QGIS is bundled within the installer. Python errors usually point to mixed installations or custom PATH entries. Remove other GIS/Python installs from PATH and reinstall via OSGeo4W.

How to reset QGIS settings?

Rename or delete the profile folder at %APPDATA%\QGIS\QGIS3\profiles\default. QGIS will recreate a clean profile at next start.