hello...i have a customer's computer doing the same. if you run a virus scan, i use AVG, u will find a virus that is a trojan.tdss.a or whatever,, !!! it attaches itself to "servicehost.exe"(svchost.exe) in the system32 part. i only know 'enough to be dangerous" but it may help you narrow it down a bit unfortunately i am going to be doing a format and re-installation of windows,updates and all
....also system i am working on is 7 home premium 64 bit. also I DID TRY USING LAN, also, so it is not a wifi issue...the computer will run all day as long as NOT connected to internet....as soon as you connect when it is ready to "ramp up" the computer then shuts down.