I have a thinkcentre M58 here who's fan speed is running constantly at 100%. To ensure this wasn't a heat issue, I checked with CoreTemp, and the CPU is running in the mid 40's, which should be more than fine. Tested a different fan, same issue. Replaced the Motherboard, same issue. Found a suggestion on this site regarding the RAM being in the wrong slot, the RAM is in SLOT1, and no change (tried every slot, no difference). The BIOS is updated to the latest, tried to Restore Defaults, no change. This is the 3rd motherboard for this system. What else could it be? I'm really running out of ideas here. Fans are full speed in BIOS and in Windows.