Lagging Problem

Everytime I leave my computer idle for even at least 15 minutes, and I start using it again, it starts lagging to the point that windows start freezing up
and I'm forced to restart it. Anyone know what the problem might be? Thanks.

If I were being a fanboy I'd be shouting LINUX IS SUPERIOR!!!11. I didn't even mention Linux; you brought it up. I am merely gloating because I find the sorry state of affairs hilarious and I wish to taunt people in their self-inflicted misery.

I don't think we need yet another flamewar on this subject, but I can't let a comment about the "popularity = security risk" theory slip by. Would you care to tell me how many worms there are that propagate through Apache vulnerabilities? That's the Apache that runs over 2/3 of the web. Now how about IIS vulnerabilities?