Dude, you are quite likely to be infected. Unless you are calculating moon-launch trajectories, or whatever, you should never see continuoous 100% CPU usage. Open TaskMgr, click application tab and see which prog is racking up the usage counter ... that's the pig to poke with Delete, but first copy the name of the prog so you can find where it "lives" in your system using Windows Search utility. Once you find the prog, check it's Properties ... you may discover who wrote the thing. Then, delete the program. Also, Run command line Regedit and determine if your Registry contains entries from the deleted prog. You really need a good AV swe that is continuously updated like Symantec, etc. Also, a hardware firewall is invaluable in keeping out the creeps who plant zombies in your system. It seems that the forces of Good continually battle the forces of Evil, both in the games we all play, and in real life. 😀
Good luck :!: