Today I got back to my dorm from Spring break. When I turned on my Early 08 Mac Pro that has been off for 10 days, the fans kicked into high gear on startup like normal... then a few seconds later, they went into overdrive and are very, very loud. The fan on the rear by the RAM slots appears to be making the most noise. I rebooted and unplugged the thing for a few hours... no luck. Upon glancing at my Activity Monitor, only 0% - 1% of CPU is ever used by anything... and it's usually Activity Monitor. However, iStat Pro indicates that my Northbridge Temp Sensor is reading 259º F. That is way too high. I can't figure out how to resolve this problem. The one small black visible heatsink on the motherboard is only a little warm at most. Can anyone help? --edit-- Resetting PRAM changed nothing.