Windows Vista: Vista REFUSES to shut down...

Vista REFUSES to shut down...

Hi all,
I've been running vista on my HP Pavillion a1720n PC for about 6 months now. Probably about 3 months ago, I would click the shutdown button and vista wouldn't shut down. It would switch to the "Shutting down" screen and then eventually start back up after sitting at that screen for some time. I never had this problem the first 3 months. I'm getting sick of having to shut it down manually with the button, I don't like doing it, it makes that stupid "unsafe shutdown" all over the place, and I'm pretty sure if I keep doing it it'll hurt my system stability. I got my first BSOD error a few days ago (although that may have been due to the fact that I was messing with GH3 for custom songs...). Does anyone know why my vista PC won't shut down properly, and what I could do to fix it?
Thanks!