NT Authority System

how can i correct problem i can turn on the computer sometimes it works sometimes it doesent…when it does..after about 1/2 hour (and this is what happens when it wont work at all) i get the message remove procedure call terminated unexpectedly by NT Authority system…i have run virus and worm checkers and supposedly the machine is clean..but then i had to reinstall operating system because this still happened..after the install..it happened again..and continues…i did read on your site of something similiar but the resolution eluded me..the person went to windows and unticked the distributed com in My Computer Properties…i cant find that at all and dont know how to get to it…any ideas???