I have a Phenom II 550 which i can unlock to 3 or 4 cores and successfully boot into windows... However, in some apps and games the PC will hard lock when i have 4 cores active, so its not 100% stable....when 3 cores are active i have no such problem, the PC is 100% stable with everything up to 3.85Gz, which is how i run my CPU, 3 cores @3.4Ghz. I simply got used to the idea of Core 4 being a dud and moved on, however Gigabyte has released a new BIOS update which allows you to turn on or off the 2 extra cores individually... Ie.. Cores 0,1,2 or Cores 0,1,3.... The strange thing is, whichever config i use the PC is 100% stable with 3 cores, which suggests that all 4 cores are 100% stable... Except that when i run all 4 cores together, the same hard lock problem occurs.... How can i have a CPU that has 4 good cores, but i can only run a maximum of 3 with 100% stability... I have tried everything i can think of, upping CPU vlts to 1.55, raising & lowering NB speeds and vlts, lowering the HT speed...all without success. My DDR2 is at stock speeds and vlts... Anyone got any ideas how 4 good cores are unstable when run together but 100% stable when run separately?