erm i had the same problem, and i found out what it was, i think it might be the same thing, its happened because "Explorer.exe" may have gotten affected, or the original path has been changed?, once your computer has booted up, and your my documents has loaded, Hold Ctrl + Alt and press Delete, then the Windows Task Manager loads up, Goto, File>New Task (Run...) then a dialog should open up Type "Regedit" then search through:
HKEY_LOCAL_MACHINE\SOFTWARE\Microsoft\Windows NT\CurrentVersion\Winlogon
Then look for a string called "Shell" double click then another dialog should open, in the field "Value Data" type "Explorer.exe", close regedit at the top of the "windows task manager" click shut down then choose Restart, after restarting see if that works, i hope it works it did for me! =] good luck let me know if it works or not, thanks!