Vista Hangs on Desktop

Hey, I've been having problems lately with Vista 649bit Ultimate edition. I can boot up the computer fine, but maybe 70 percent of the time once it hits the desktop it will hang. At first it looks normal, but as soon as I click the screen gets a white sheen over it and the mouse cursor turns into the blue circle that keeps spinning. It then says "windows explorer is not responding." If I click "wait for program to respond," then after a few minutes it goes back to normal.

Does anyone know why it suddenly started doing this? My specs are pretty standard (all at stock speeds):
GTX 275
Q6600
8 gig G. Skill RAM
150 gig WD Raptor
500 gig Seagate Baracuda
700 W OCZ Power Supply
Asus P5E I Think, maybe P5Q

Start-up Programs are:
Rivatuner
Steam
McAffee
Print Key 2000

One hypothesis I have is that its Rivatuner. I don't know if this is normal with Rivatuner, but everytime I upgrade the graphics card drivers Rivatuner does not recognize the new driver. Whenever I re-install Rivatuner, no matter what I do to delete the old one it always seems to still be there.

I have used McAffee and Malwarebytes to scan for viruses, but they have found none

Any help will be MUCH appreciated, I'm afraid to click on my desktop now because it seems like every other time freezes the computer.

Thanks!

Have you tried the Task Manager and Resource Monitor?

Poking arround there may give you a clue. It's always good to learn to use those utilites, especially when you have a lot of odd software running.