I have a 2009 Xserve, which has been doing just fine. Because of some issues I decided to reset the SMC. I did that by properly powering it down and then disconnecting the power cord and plugging it back in a while later (> 15 s) and hitting the power button on the front. That’s when one of the fans (or all of them) began spinning out of control. I was able to boot up and shut down without problems, hoping that running the proper OS code would get the fans under control. On subsequent attempts to boot it up, the server just power-cycles with the fans spinning up and it resetting itself, before I even see the gray Apple.