Unlock 4 cores AMD 555 BE

I honestly can't say what that error means, but one slight possibility is that your motherboard won't support that cpu unlocked. Your board can only handle 95W cpus based on the support list, an unlocked Phenom II X2 becomes a 125W Phenom II X4.

loneninja, thanks for quick reply.

The AMI bios 78LDU412 on the MoBo supports CPU unlocked, on the Bios start-screen I saw that it displayed "Phenom X4 B55" and the core count is 4 but it fails when starting load system (Win7) with the error message: ' The header file possible corrupt, the header file check-sum does not match wit the computed check-sum" and the system halts.

Do you know where can I check the cpus power like you said?

In the Bios setting I saw the option that I can set the cpu voltage.
It has the setting:
CPU Over voltage: Startup(default)/ +7,8%/+15%/+23%

Try unlocking one core of a time, first core 3 then core 4.