I know that not all will unlock but after reading many posts it seems that the majority do. My MB is a GB MA785GM-US2H running Win7 64bit. Runs fine as a dual core but with all 4 cores unlocked and with my ULTRA 500W PSU it won't boot (it will POST) into Windows. I was able to disable core 1 and unlock core 2 and 3. Now it shows as a Phenom X4 B55 with 3 cores. After some more reading, I suspected I had a PS problem because my PSU only had a 4 pin CPU power plug (MB has an 8 pin). I bought a ANTEC 500W PSU which has a dual 4 pin CPU plug. With either the 8 pin or 4 pin plugged in, the computer would POST but not boot. Just a blank screen after with Windows logo started to appear. I put back in the old PSU and can still boot and have a triple-core. Do you think with a better/higher wattage PSU I could unlock all 4 cores?
Did you try increasing Vcore? I don't know how your mobo supports unlocking, but your processor may not be getting enough voltage to be stable with all cores unlocked. Or you may just not be able to unlock all 4 cores. If not, 3 is still better than 2!
My MB supports overclocking by enabling ACC. Interestingly you can only control the 3rd and 4th core once you enable ACC but even if do that and I disable 3 and 4, it will not boot (it always POSTs). You have to get control of the first 2 cores before enabling ACC. After that you can enable/disable cores 2, 3 and 4 individually.
I tried increasing the voltage but windows will still not boot past the logo screen. I can overclock the snot out of the 3 cores (4.x ghz!) though. I think it's weird that a brand new PSU (it could be defective) with the proper power connectors for my MB will not boot even with just the stock (2 core) settings when my 3 or 4 year old ULTRA will. I might just settle for 3 overclocked cores (need to get better cooling).