Shut down problems

I dont think that I posted the problem that I am having correctly. I am going to try again.
The problem that I am having is that when I try to shut down my computer. For thirty minutes or so the computer freezes. After my thirty minute wait the computer just restarts. It seems that the only way I can shut down my computer is by pushing the power button. I am using Windows XP home edition with SP2. I am looking to find some advice as to why this is happening and how can I fix the problem.

 

Did you check for spyware/malware or viruses?

 

Yes I ran my virus check and I used adaware.