Portege 3500 shuts down

If it's going into thermal shutdown, this is an easy fix if you're comfortable with taking your laptop apart. What has happened is the thermal grease in between the cpu and the heatsink has dried out, and is not conducting the cpu's heat properly. The machine is shutting down to protect itself. My best advice is go to any computer store, and get a tube of thermal paste, and find the disassembly instructions online. Clean both surfaces (the heatsink and cpu) with rubbing alcohol. Re-apply a thin layer of new thermal grease, and reassemble. Be sure to clean the crud out of the heatsink while you have it out.

its difficult to identify the problem but there two things that might cause this...first, virus, your laptop may have been infected with a virus e.g. brontok....try restarting your laptop and boot on safemode. if it works there then a virus is causing the issue. you just need a scan and delete it with an anti-virus. second. you are having a problem with you fan/processor. this would be the time to go to the nearest PC repair shop.