Computer is a Lenovo TC M52 P4 / 3.2 - I have added a sound card, a PCI express Geforce graphics card and a NIC card. The problem seems to be overheating as it only shuts down like this during the summer months, and then only later in the daytime when temps are highest (ambient room temp is no more than 75F). It shuts down with no warning (fan speed does not increase) then it restarts - that is when the internal fan really kicks in - but the computer usually shuts off again within about 30 seconds. If I leave it off for a few minutes, it comes back on and works OK but then usually shuts down again. I found if I put a portable fan blowing towards the back of the computer (or pop open the case and leave it open) the problem goes away. It seems like the fan speed should increase before the computer shuts off, but the fan only cranks up AFTER the first shut-down. I could get a stronger fan, but if it is not coming on until after the initial shut down, is there something else I should be looking for?