Okay... no usb devices...
Another thought... disable fast shutdown (if you haven't already).
To do so: go Start, then Run, type in msconfig. press okay
Then a menu pops up. Under the General Tab, click "advanced"
put a tickmark in disable fastshutdown... press apply/okay, then reboot computer, see if that helps.
Also, make sure you windows temp folder is empty.
good luck!