HI Dominique,

There can be multiple reasons for the broken Start Menu and as usual, one solution cannot fit everywhere. Still, you should definitely give the following a try:

1. Open Windows PowerShell as Administrator
   1. Right click Start button
   2. Choose Command prompt (Admin)
   3. Key in Powershell in the black window and hit Enter
2. Paste the following command in the Administrator: Windows PowerShell window and press Enter key:

   Get-AppXPackage -AllUsers | Foreach {Add-AppxPackage -DisableDevelopmentMode -Register "$($_.InstallLocation)\AppXManifest.xml"}

3. Wait for PowerShell to execute and complete the command. Ignore the few errors (in red color) that may pop up.
4. When it finishes, try hitting Start and hopefully it’ll start working.

You can also try the below methods as well: 

1. Sign out and Sign in
Sign out and Sign in or restart your PC and see if the problem goes away.
2. Automatic Repairs
If your PC prompts for Automatic Repair, continue with it and let Windows carry it out.
3. Kill and restart the Cortana process
If you find that Cortana is not working properly, the best thing to do would be to kill Cortana process and restart the process via Task Manager. If it was a minor runtime error Cortana would just take a restart to fix it.
4. Disable Antivirus software
Some security software are known to create this issue – Avast for instance. Disable it and see if it makes the problem go away. If your security software is the culprit, make sure you are using its latest version – else you may want to change it.


I hope this helps.

If it doesn't solve your problem, revert back to me and I will provide further assistance.

Regards,
Lokesh