There is a temperature limit switch that is likely responsible for this shutdown. If you are able, take the tower off the stand and split the case (probably a half dozen small Philips screws to remove). Look for an accumulation of dust in the area of the limit switch or on the vertical fan assembly. If you have an air compressor you may use a blower nozzle carefully to clean where you cannot reach in the fan cage. Reassemble completely before testing. Do not do any test with the case opened/off.