NT Workstation is slooooow...

[Turczinator]

I have an NT Workstation here at work that is slooow. What I mean by slow is that with just the explorer window open a right-click to get a pop-up menu takes about 30 seconds to occur. Applications are starting to run slow also. I've swapped memory from another PC of the exact same configuration (both are PII 450Mhz, 256M) to see if that was the problem, but it did not solve it. The second PC ran popup and apps fast after the mem swap, but the slow PC was still slow. I've defragged the HD on the slow PC with Diskkeeper four times, but still slow. I've got 12 PC's all of the same brand/configuration and this one's performance has started to drop off. Any thoughts?