Windows Just Locks Up (Desperate)

Hello,

I am so tired of this already. My PC just locks up at random times and I am not doing anything imparticluar. My mouse will just stop moving and all windows are still there but i can no longer move them. The screen is just still. I have a Dell Dimension 8300, P4 with Hyperthreading. I have an ATI 9000 Radeon, SB Audigy 2, Sony DVD-RW, and some apps installed, mostly anti-virus and video capture items such as Pinnacle Studio 8.

Any help would be MUCH appreciated!

Thanks,
Adam