Update: The problem seems to have stopped. It hasn't happened in two days and everything I've previously done that seemed to have triggered it is no longer producing the same results. I honestly don't know if it's gone or just hibernating, in a sense. As someone in the industry I personally hate it when bugs just magically fix themselves, but... I'll post back any further information when/if I have it. I don't consider the problem solved, just dormant.
I'm experiencing the same problem since running Windows 10. The problem is, that i cannot reproduce it clearly. Sometimes my machine runs two weeks absolutely flawlessly and then there are days, where I must reboot every 5-30min after Startup. The Applications i started keep running, but the Start-Button becomes unresponsive. I cannot kill the explorer-process, too, when this arises. Task-Manager says: Access denied. I'm running as a user being in the local Admins Group and UAC is turned off.
sfc /scannow says all ok besides some opencl.dll-checksum-error of my nvidia graphics driver, which seems to be a common problem but has nothing to do with my start-button-problem.
I had this Problem with Windows 8, too, but it stopped occurring, when i installed Windows 8.1. After (clean) installing Windows 10 the problem is back again - with and without 1511-Update.
Quote