Continued problems after a clean install

I had been running windows 7 RC since I upgraded my computer a couple months ago. I was running fine until about three weeks ago, when I started to notice certain programs or activities were taking a long time to load.

The first program I noticed it with was Itunes (yes I know its a horrible, bloated program, but it's compatible with my ipod so I use it). It would take a good 10 to 15 minutes after clicking on the shortcut or the .exe for itunes to launch and sometimes it wouldn't launch at all. I tried reinstalling itunes, to no avail. Then I noticed when trying to open My Computer, it would act like it was loading (with the green loading bar up at the top) and it would take at least 5 or 10 minutes for me to be able to access my hard drives. Sometimes, my hard drives and cd drive won't even appear and it will be stuck loading for a long time.

The first thing I thought of was a virus, so I ran Avira scan and malwarebytes, both of which froze. I was getting pretty freaked out at the time, thinking I had a pretty bad virus. As a last resort I tried reinstalling both of the programs, which for some reason worked. I completed both scans with no problems, and the problem persisted, and I encountered it in the control panel, as well as launching diablo II. Everything else was running fine. I was getting pretty pissed off and by now couldn't wait for windows 7 to be sold by my school so I could do a clean install.

So two days ago I went out and bought windows 7 ultimate from my school for 10$ and did a clean install. Everything seemed to be working fine until I noticed it was getting sluggish again yesterday. I clicked itunes exactly 30 minutes ago now and it still hasn't launched. My computer is beginning to be sluggish again, and diablo II wont launch. Oh and itunes finally launched. 32 minutes after initially clicking it. I am at a complete loss on what to do, so i figured, as a long time reader, I would post something here. I have googled numerous things and have not found anything similar to my problem, except for one dead end thread somewhere. So any help would be appreciated.

Im running:
Windows 7 64 bit ultimate
i7 920
6gb mushkin redline mem
gtx 275
evga x58 classified
1 tb western digital caviar black

If anybody wants me to list all the programs I have installed on my computer I will, but that will take a bit so I'll wait for a requestto do that.