Remove the side of your computer using a cross-head screwdriver. Now you will see a motherboard, which is a big circuit board, with lots of little components mounted to it. Loads of shiny (or prehaps not so shiny - in your case) transistors. You should (if you computer was built right and has not been tampered with) find a fan screwed into the top of a headsink. If there is not a fan, get down to radioshack (US) or Maplins (UK) and buy one, or they can be picked up on ebay for about ÃÆââ¬Å¡Ãâã5. If you do actually have a fan in there, unscrew it and remove it. It's probably covered in dust, hold the fan still and blow or wipe out all of the dust. The heatsink should now be visible. Blow all of the dust out of that and any dust around other components. re-assemble and re-boot (making sure you have not got any screws left over :XD: ) If it still switches off, try without the side panel on, if it switches off after that, you've established a problem with your computer, not with cooling or overheating. I'm not to clever with the other side, but try and do a quick virus scan. If that does not help, consult another member, they may be able to help you more with the virus/trojan side of computer management.