I bought two processors X5492 3.4 Ghz to 3.1 then updated my mac pro with 2x 2.8 ghz, but when the computer does not display anything on screen. I have understood that should work. As I can make them work? Has anyone tried to do this upgrade? Computer settings you have? My computer: Model Name: Mac Pro Model Identifier: MacPro3 1 Processor Name: Quad-Core Intel Xeon Processor Speed: 2.8 GHz Number of Processors: 2 Total number of cores: 8 I L2 cache (per processor): 12 MB Memory: 16 GB Bus Speed: 1.6 GHz Version of the Boot ROM: MP31.006C.B05 SMC Version (system): 1.25f4 Software OS X 10.8.5 (12F45) ATI Radeon HD 5770 1024 MB Memory 16 GB 800 MHz DDR2 FB-DIMM Thank you all!