Hi there. I have a refurbished Mac Pro 5,1 (mid-2010). I just recently grabbed a pair of Xeon X5690 SLBVX 3.46GHz chips and had a friend install them. Since the install, my fans have been running full-tilt - resetting the SMC and PRAM has no effect, and I took off the heatsinks to make sure nothing had disconnected or obstructed their thermal sensors. The machine also does not chime when it starts up. I took the machine in for a diagnostic and just received it back; the tech said that "the machine is not receiving thermal information from the CPUs" but would not elaborate when I asked WHY, or if there is any other solution than "put the old chips back in." As with any of this stuff you hear a lot of different theories from different people so at this point I'm pretty confused... Now I'm hearing that there may be compatibility issues deeper than "make sure you get the X5690 SLBVX model" - I'm going to peruse the CPU compatibility thread in this forum and try to shed some light on that. Would sharing the machine's serial # help gain insight on potential compatibility problems? I'm just really hoping there is not some deeper compatibility issue, and that this is something I can solve without having to buy another set of CPUs. Any insight would be hugely appreciated, thanks for your time.