Processor problems can vary from incorrect fittings of the cooling fan, to minor problems in the bios settings. Critical problems found are the cooling fan heat dips leading to breakdown of the PC. However, P4 and even the Athlon, can run with only a heat sink and no fan, but I wouldn’t advice this. The processor can overheat, breakdown, or even drop in performance, if the CPU fan breaks down or is filled with dust.
Sometimes, even the power cables inside the chassis touch the fan and stop it, leading to overheating. In this case, open the chassis, check for any cables, which have got in the way of the cooling path or the fan. Also regularly keep your PC free from dust inside, as well as the surroundings. Use a blower (something like an AC blower or the blowing end of a vacuum cleaner) to blow away the dust from unreachable corners. Be careful whilst doing this as you may damage the delicate components, and even the fan blades. This is necessary if you are situated in a environment prone to dust. Do this at least once a month. Assure that the fans inside the computer are clean and dust free.