the tower case is not the cpu . The cpu is the processor chip inside .
It has a fan that might be clogged with dust after 6 years an that can cause windows to shut down to protect components .
First thing to try is disconnect from the power , take the side of the case off and clean it with a can of compressed air to blow all the dust out .
DO NOT USE A VACUUM CLEANER , or a brush
then plug it back in with the case side still off and see if all the cooling fans are spinning