I also tried 2 solution. But It doesn't worked.
and
CamStudio application was the issue in my case.
Somehow it reserved this key to itself and Visual Studio was not able to use it anymore (I've tested it MS Word (Alt+F10 - was working as expected, while CamStudio was on - when minimized it appears only in SysTray)).
I've closed CamStudio and it was fine:
F10 functionality "reappeared" in VS2008.