Building on my previous thread: http://www.pcmech.com/forum/showthread.php?t=214360 I ordered an Optiplex 745 motherboard off eBay and then plugged in my old components from the GX620 machine and Windows 7 Pro 64-bit runs beautifully. The only problem I have is when the system first boots up, I get the error: Alert! Air temperature sensor not detected Press F1 to continue and F2 to enter setup There is no way to disable this warning (confirmed with Dell), so whenever the system reboots F1 must be manually pressed (a problem if working remotely). If I press F1, the system runs fine. The case fan seems to run at full speed the whole time (I guess because it can't determine the temperature to throttle itself), but overall the system is very stable. I did a bit of testing using an existing 745 we have and after swapping out case fans, I found that this component is not the problem: the fan from the GX620 system works with no error in the other 745 system and the fan from the 745 gives the same error in the new 745 system. So the problem is either: a faulty motherboard a result of GX620 case components not being fully compatible with the 745 motherboard I want to see if anyone who has any experience with something like this has some feedback on what you think the cause may be.