On a number of occasions the Windows start button stopped working on computers running Windows 10 on this side. You might find a number of possible fixes online for this issue, but this one works here:

1. Open the Task manager (Press Ctrl+Alt+Del).
2. Click File > Run New Task
3. Make sure you have a check mark beside “Create this task with administrative privileges” Click “OK”
4. Type CMD. Press [Enter].
5. Type the following three commands at the CMD prompt, press [Enter] and wait for each to finish before you move to the next one (Tip: copy the last one):
dism /online /cleanup-image /restorehealth
powershell
Get-AppXPackage -AllUsers |Where-Object {$_.InstallLocation -like “*SystemApps*”} | Foreach {Add-AppxPackage -DisableDevelopmentMode -Register “$($_.InstallLocation)\AppXManifest.xml”}
6. Close the CMD window
7. Restart Windows.