I don't see any make, model but if it's a desktop I power down and unplug the mouse and keyboard (on a laptop it's mildly harder to do this) and try again. I've lost track of stuck keys.

http://answers.microsoft.com/en-us/windows/forum/windows_vista-system/computer-shuts-down-slowly-and-boots-to-advanced/0ad7b51e-e1ae-46ba-880a-0d6d7b540fe2 repeats the SFC but with a twist about RUN AS ADMIN.

An infected boot area could do this but before we try to repair that I have to write to be sure your backups (plural!) are current. Then go get EASYBCD and repair the boot areas.