|If this is a desktop computer.... |
It sounds like the bearings on your cpu fan are in bad shape.
You probably need to replace the cpu fan.
If this is a laptop or netbook computer.....
It sounds like the bearings on your fan inside the case are in bad shape.
You probably need to replace that fan.
If that fan doesn't spin or spins too slowly when you first boot the computer, most bioses will shut down the mboard within a few seconds when no rpms or not enough rpms are detected, to prevent the CPU from burning out.
That's more likely to happen when the room temp is cooler.