Blank Screen/Desktop on Boot

[iceangel89]

i recently got just a blank black screen/desktop after boot (i still see the welcome screen then blank (with the Windows 7 Evaluation copy ... stuff))

i have restored the backup image i have. but what might it be caused by? in XP sometimes i see such things happening. but i havent in Vista, this is the 1st with Windows 7. in XP i just need to ctrl + alt + del and run explorer. but in this case, windows 7, ctrl + alt + del doesnt work