especially on the fans and heatsinks, get a can of compressed air for that. also make sure the CPU fan is working. pull a side cover and try a cooling fan to blow air directly into the case.
My PC shuts down on its own after about 30mn of use.
It shuts down suddenly as if the power plug was pulled out, and then it won't start unless I leave it for at least 2 hours.
Any idea what the problem might be?
I was told it might be because it's overheating, so I vacuumed the inside to get rid of the dust, but it's still acting the same...