Start it up, and at the question, go to continue booting into safe mode. Then try shutting down. If on reboot, you still got issues, probably got a virus or something.
If so, run your anti spyware and any other malware programs, and then use a previous system restore point say a day or so before the pc started going bananas.
Alternatively, it could be a part of the pc not working properly (i had this recently with a fx card who's fan had choked up with dust, leading to overheating, making the pc unstable and causing crashes requiring power off without shutting down, a few of these fubar'ed my pc, but a new card, and the above, resolved the issues.
If none of the above works, then you might be stuck with reinstalling windows?
I had this recently.