Hi, sorry for the double post, maybe some readers will only get it here Hi everyone, new to this forum. Mac pro 2009 mono cpu (stock mono 2,66) updated to 5.1, high sierra with bootrom MP51.0089.B00 BootROM CPU update fail !! Trying to install a x5675 bought on ebay After cpu change and new thermal paste, at first boot I had a apple logo + progress bar stuck at 75%. Did a pram and smc resest (several times, event 10 times pram reset) no success. verbose mode says "unsupported cpu unsupported pch" Tried to boot with latest sysrescuecd linux live, gave me a kernel panic at boot with cpu blabla problem No red light in the cpu tray board Pictures for the verbose mode Strange thing : after the FIRST pram reset the verbose told about the cpu family, model number and speed, never after that. Any clue ?