>>When I did the search I was wondering if McAfee might be the problem. But that doesn't seem to be the situation in your case. The links point to one or more MS updates that seem to cause profile problems for some people, which are similar symptoms to what you're seeing.
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>Yes, the one ending with 355 has been reported. That was the first one I removed. This did not change anything. Then, I removed everything up until April 4. This is when everything was ok. That did not change anything. More than 49 updates were removed. Then, I reinstalled them again. This is still a no go.

If your profile is corrupt you could try a repair. Googling [windows 8.1 repair profile] brings up some ideas such as http://southpawprints.wordpress.com/2013/12/14/windows-8-1-corrupt-profile-the-good-bad-and-ugly/ , http://mywindows8.org/fix-corrupt-profile-in-windows-8/ .

It might also be a corrupt security Access Control List (ACL). I don't see many useful-looking hits Googling [windows 8.1 repair acl].

In a perfect world you would have an image backup from prior to the problem arising. Note for lurkers - Windows 8/8.1 still has image backup but it's a bit hidden: http://winsupersite.com/windows-8/windows-81-tip-use-system-image-backup . However you would in advance have to save any new user files since that image, restore from the image, restore your user files and reinstall any newer programs and updates.

If none of the above, or any other magic trick work your best bet is probably to open a telephone tech support incident with MS, as I suggested earlier.