That sounds to me like either the processor overheat alarm is going off, or the CPU fan has failed.
Open the PC and check all the fans to make sure they're spinning okay, and look at PC Health (or similar) in the BIOS for the temperature of the CPU.
If it's above 70C then you have a problem- time to remove, clean, and reapply the heatsink. Don't forget some thermal goop, applied in a 1-2mm-thick layer onto the bottom of the 'sink before you do so.