Is it overheating? What are the temperatures? Can you go into BIOS and look at the readings. Press delete or F5 or F8 when it is turned on.
I'm not a PC expert, but I would say Motherboard 30-50C is OK (>70C would be a concern if it was my machine).
If it is too hot, assuming the fan is working on the CPU, it might be a poor contact on between the heatsink and chip. Search the internet for the best way to apply the thermal paste etc., or PC World sell this as a postage stamp size patch to take the guesswork out of squeezing a guessed amount out of a tube.