This could be several problems. If the CPU fan is connected to the power supply directly (instead of the motherboard) then it's probably a fried motherboard. If the CPU fan is connected to the motherboard and still getting power, it could mean that t...
Try to reseat the internal power cables to the motherboard, and the cables to the power supply. Try a power supply tester to see if the PSU is dead. Try to leave it overnight, in case it had gotten too hot, so all the heat can dissipate. Other than t...
I have one just as old, another even older. Could be your power supply. However; could be in the BIOS, processor fan, registry, software and/or hardware. You do not state if you have run any cleaners and or optimizers, so it could also be a registry ...