Make certain the CPU heatsink/fan assembly is securely fastened to the motherboard. The hs/f should be sturdy in its mount and not rock or wobble. If this is an Intel sys, the pins/screws in all four corners must be secure. If an AMD, make certain both ends of the clamp are held fast to all 'dogs'.
Access system BIOS. Look for a section titled Hardware Monitor or some such. Note the CPU and system temperatures and the temp alarm points. Post here.
Access system BIOS. Look for a section titled Hardware Monitor or some such. Note the CPU and system temperatures and the temp alarm points. Post here.