Windows 8 : Hyper-V Platform unchecks

Hi all,

after enabling all Hyper-V Features within Windows 8 (RTM) the Checkbox for "Hyper-V platform" unchecks itself.

After enabling the Hyper-V platform Feature and restarting the PC it does some restarts by itself. As soon I can logon again I realized all Features but the Platform are checked and installed.

When enabling the Checkbox again - without restarting - but looking again into the selected Features its unchecked automaticly. 

I already checked the SLAT and DEP Settings. Assuming wrong or missing BIOS Settings would gray out the Checkbox, but it is not.

I have no ideas anymore.

Thanks for ideas,

Jan