run checkdisk and a virus scan
+1: If your CPU is going crazy, it isn't a hardware problem....most likely a software issue. Check disk will find out if your hard drive was damaged when transported (needle might have hit the disk which will hickup when trying to read from it...usually results in quite instable/errors coming up operations. I'm more on the "trojan/virus" side...your friends may have had a trojan that transmitted during the lan session.
If you gamed and used "free" software to communicate, well, free isn't always free. If even one of you played the game "a hacked/cracked version" then he/she might have carried the infection which gave it to all of you. DAMN LAN TRANSMITTED DISEASES!!!
If you have patience...reinstalling windows properly could get rid of the issue...though it's a pain in the @.