Windows 10 start menu key left click options not working

all fixed now ty for your help dsim solves a lot of stuff

scannow found a corrupt file and repaired it no probs

I just had the same problem and I solved it.
Clicking any other program and everywhere else in Windows 10 worked fine, but for some reason left clicking on Windows Start button would not display the normal menu.
Here's how I fixed it.
1. open task manager
2. go to Details tab
3. find explorer.exe (yep it's the windows 10 shell)
4. kill explorer.exe (highlight the item and press delete key) -- yes, you can really kill explorer
5. Now you'll only have a desktop and taskmanager running.
6. in task manager choose the File...menu and choose Run new task...
7. type "explorer" and press <ENTER> this will start the explorer shell again
8. now try clicking your Win 10 Start Menu and it will work again.