Do a [ctrl]/[alt]/[del] ... Once. A window will come up showing everything that is running.
My bet is that you have countless instances of "svchost" running, each taking a piece of the action. There is a trojan that uses svchost once it gets in. A year ago I had this problem. I searched for directions to stop the thing that was causing svchost to spawn uncontrollably. It's really sneaky. I finally reinstalled XP from backup to get rid of the thing.
In the meantime, You can stop all instances of svchost one at a time, to speed things up. A crude way of dealing with it, but it works.