First, determine if the keyboard button still works or not by pressing the Windows key. If yes, then your mouse may be causing the issue. Simply unplugging the mouse and plugging it back again should fix it for good. If not, you need to get the mouse replaced as soon as possible. Other times, even if you restart the PC your start button may still not work correctly. This means your operating system is causing the issue instead. Below you will find some of the popular fixes arranged from simplest to complex.
Start Button Not Working Windows (Fixes)
Logout From Your Account and Log Back in
Restart Windows Explorer in Task Manager
Use Sfc Utility
Using DISM Utility
Use Taskkill Command
Turn Off Game Mode
Turn Off Filter Keys
Fix Cortana by Rebuilding
Check for Updates
Run Antivirus Scan
Use Registry Editor to Fix Values
Rebuild Index Across All Drives
Reset Your Pc
