There is a new massive virus called sassor that attacks random computers who havent updated their maching with the most recent critical update.If your computer reboots over and over without you ever getting a chance 2 do anything heres what u do.When u start up your computer you should have at least 2 selections 2 choose from that are highlighted before you even get 2 your logon screen.Dont use the 1 you normally use go 2 the other 1 below it or above it depending on which 1 your using.now select that and logon and if all is ok go drectly 2 microsoft update then go 2 norton.com and get a virus scan.next download lavasoft's adware at lavasoft.de and do a sca nafter you've gotten the latest virus refrence file.if you find anythign quarntine it not delete you quartine that bitch immeidately.now after you've removed the problem try restarting your comp and now try your original and if its fixed then yea.If this didn't work try login on windows with safemode and hope 4 the best because e thats all i can say.Also another thing if it still persist try going ctrl-alt-delete check your processes delete any that are not reconizable such as lsas.exe which ithink is the name of the sasser worm.And finally if ur still stuck wipe your drive if ur on a network dont let it spread 2 anbody else in your work/home.
Best of luck ~koftr.