Machine Mac Pro 2009 - Quad core. Symptoms: Red light on processor board, no boot, no fan in CPU heat sink. Also can see red-light on CPU-A heat on backboard. The other case fans run excessively and loud. Diagnosis: Failed Heat sink fan. Also failed was the rivets on the Northbridge heat sink Fix: Items: New CPU heat sink New Northbridge heatsink rivets from ebay (keywords: heatsink spring rivet) Work: Installed Northbridge heatsink with thermal grease used ShinEtsu MicroSi - Came with heat sink. Installed CPU heatsink Installed CPU tray into Mac. Runs perfectly. CPU temp 34, Northbridge temp 47.