This same crap happen to me on vista,but every thing used to get disabled,if i restart the whole system hang after a 2 sec in windows,within those two second i opened Google chrome and whole system hanged except Google chrome,so i browsed and i checked out somethings and it was a damn spyware,some process running in the background,i had to download a third party task manager,and disable the process from there some anti virus also have task manager like kaspersky.try this and see if some process in blocking the task manager.