When critical Windows system files are missing or corrupted, your operating system may begin to malfunction. Common symptoms include Windows features not working properly, system errors, or Windows becoming unresponsive or freezing.

Here's how to do that on Windows, Mac, or Android.

Use this tool to find and remove specific prevalent threats and reverse the changes that they made (see Covered malware families). For comprehensive malware detection and removal, consider using Windows Defender Offline or Microsoft Safety Scanner.

Get Help has troubleshooters, or diagnostic tests, that can check your system configuration for anything that might be causing issues using your devices. View troubleshooter results. After you run any troubleshooter, Get Help provides details on any findings and suggestions for possible remedies.

When you select an AppFix, you can start the program executable (.exe) file, and the AppFix is applied. If a suitable AppFix is found, the tool eventually helps you generate and test matching file information.

Microsoft Defender Offline will load and perform a quick scan of your PC in the Windows Recovery Environment. When the scan completes, your PC automatically restarts. Note: To see the results of the offline scan, open the Windows Security app on your Windows device and select Protection history.

In Windows, use Search on the taskbar to search for PC Health Check, then select it from the list of results. If a PC Health Check update is available, you can quickly install it for the latest version.

Get Help has troubleshooters you can run for many common scenarios. These often help resolve issues without the need to contact support. If a troubleshooter is available for your issue, select Start to run that troubleshooter. After you run any troubleshooter, Get Help provides details on any findings and suggestions for possible remedies.

Learn how to use the DxDiag.exe tool to collect system information useful for troubleshooting problems with Microsoft Casual Games.

The test mode message indicates that the test signing mode of the operating system is started on the computer. The test signing mode may start if an installed program is in a test phase because it uses drivers that are not digitally signed by Microsoft.