i had a really bad virus once...it raped my computer hard...core...in the sides... it infected my prefetch folder so everytime i opened a program that i used often i raped myself hard...i lost the ability to see user accounts, add/remove windows components, and other things... because i lost my user accounts i couldn't install certain programs... in the end i had to reinstall my OS 5 times before i realised a virus was on one of my backup cds... AVG is my best friend...