In the case of Avast at least, once you switch the shields back on, the Start menu search may continue working as it should. You could just try disabling your Avast shields temporarily, which should get the Start menu search back. ( Windows Defender itself has become a viable, secure option in recent years.) Avast is one culprit, so try uninstalling that if you have it, then find an alternative if need be. To be clear, we’re not suggesting here that you should disable and completely remove all third-party antivirus software from your device, but based on feedback here and across the Internet, certain programs cause Windows Search to malfunction. Disable/Restart Third-Party Antivirus, Enable Windows Firewall

In addition, running the SFC utility in Windows 10 Safe Mode could solve the problem for you, so that’s worth a shot if doing it in regular Windows 10 fails. SFC, known as System File Checker, is a utility in Windows that allows you to scan for corruptions in Windows system files and restore them. Give that the Start menu search is a system process, any errors in it should be detected by using the SFC utility. If Windows Defender will not turn on Windows 10/8/7 and runs into an unexpected error, perhaps there is something wrong with your system files. This will scan your system files for any errors and corruptions and automatically attempt to fix them.

Windows 10 action center not opening