For a few reasons. Most of the time it's the drivers issue. I get to hit Dell for motherboard and such drivers as well as remove any mouse and keyboard drivers the owner installed. I want the maker's motherboard, USB drivers and NO KEYBOARD OR MOUSE DRIVERS other than what Microsoft installs.
THIS HAS HAPPENED IN XP TO W10. It is not a W10 exclusive problem and very upsetting to many owners because I don't have a step by step. In forums I can only guide. You have to deal with the steps to get there. Sorry about that but with PCs all over the map, this is how I work this area.
Now there is a second cause I run into and it's some app or infection. KEYBOARD LOGGERS can reveal themselves this way as well. I like to use Grif's advice at
http://www.cnet.com/forums/discussions/how-to-remove-pup-option-603542/#post-f742c795-5881-433b-a29b-6d758efe5cd3 to see if there are such.
Finally once in a while you will get a bad mouse or pad. To test this I start by pressing the Windows Key to see if the Start menu stays up. If it does I pull out my mouse from my PC Medic bag (I carry the usual tools you see techs carry there.) Some think it's my Felix the Cat's magic bag.
Good luck,
Bob
After being forced to install Win 10 from win 7, I’ve had nothing but problems with Win 10 start menu and apps.
For the first couple of cumulative updates for Win 10, it worked okay.
Then, after one update the start menu and Win 10 apps won’t work.
I’ve tried every suggestion on the net and used every Microsoft checker they have and nothing fixes it.
I made a short video of the problem and posted it in my Dropbox : https://www.dropbox.com/s/qi42lhghhnlkkj5/Win10.mp4?dl=0
The first shows the ‘Shutdown’ being left click, which nothing happens, then right clicking with the option window just flashing.
The second shows what happens on right clicking on an app to remove, etc., which just flashes.
The third shows clicking on the ‘Notification’ icon which just flashes.
I’ve had to install a 3rd party start menu to use.
All my other programs work fine, just the Win 10.
Thanks for any suggestions…

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