Big cpu usage problem

Hey there.
I have a serious problem.
Every now and then(I have no idea on the recurrence of this problem), a process(never the same one) starts taking 50% CPU usage(that is, taking a whole advantage of 1 core, I use core 2 duo). Plus, the program of the process is not responding. So I close the process of course.
But then, another one starts doing the same thing. Mostly the second one doing it is a program I just clicked on. so, let's say the first one was Firefox, and then I clicked on the start menu, so explorer.exe will take 50% CPU.

I have defragmented my disk, used all the windows updates, checked the avi files program, and nothing. it doesn't help.

I'm hopeless. Any advice?

Thanks.

>>1
>I'm hopeless
/thread

Uh, just do a clean install of Windows like a normal person.  Generally troubleshooting obscure problems like these takes too long.

Also, have you installed anything recently that might cause these kinds of fuckups?

The Phantom Dumper strikes again! This time, at my office job. It was me who took the upper-decker in stall 2 of the womens bathroom. It was me who shat in the upper right hand drawer of the VPs desk. That horrid smell in the copy room? You guessed it. I took down a ceiling tile, crapped, and put it back up. The cute new intern? It's my fault she left. She left her purse in her cubby overnight. Yep, I got it. The office managers coffee cup? I apologize for this one because I had Taco Bell. Oh, and that wasn't dog shit sitting in a nice pile on the sidewalk leading to the main entrance. Come on, when was the last time you saw a 250 lb dog? The shitting will continue until I get that raise I was promised 6 months ago.
And the next round will be worse, since I've started drinking Metamucil