After two months of no problems, no programs like IE or Windows explorer will run...instead I'm ask to choose a program to open with. If I go to the same program and click run as administrator, everything works fine.
The paths are OK, and sometimes the error is explorer.exe not found, but the exe is in the ....System32 directory.
I did do several virus scans, but had no serious hits and all the minor items were removed
sfc/ scannow came back clean!