Anyone who overclocks the processor (CPU) or Graphics card (GPU) is probably smart enough to take their computer apart and give it a good clean anyway
They tend to overheat in enclosed spaces too (i.e. cabinets)
Symptoms could be:
- Computer crashing often
- Hard drive switching itself off (sound like a spaceship landing)
- Computer suddenly switches off and won't switch back on again. If you experience this, switch it off by the mains for 5 mins and then try and switch it on again.
If you are going to open up your computer, be careful.
Ensure it is switch off and un-plugged at the mains first.
Discharge any static electricity by touching anything metal i.e. radiator or the unpainted parts of the computer case.
I wouldn't recommend using a hoover or any type of mains vacuum devices as these can cause static electricity (especially belt driven hoovers) which if discharged on an electrical board, could cause damage.
I'd recommend buying a can of air available from most PC shops for a couple of quid.
If you're not confident enough, just make sure that there is a bit of room around the case and fans for hot air to dissipate, and if your computer doesn't need to be on, switch it off - saving electricity too!