CPU core suddenly locked?

I've had no real problems before now with my AMD Phenom II x6 1100T Black Edition. It's been able to handle pretty much everything I've thrown at it, and when I first got it I put it through the ringer with Prime95. However, on my last few reboots I've been seeing that only 5 out of 6 cores are unlocked. Why did one suddenly lock like that? I could try just unlocking it, but is there a way to tell if it's actually damaged or what else could have caused it to become locked in the first place? If it is damaged, would unlocking it risk further damage to the CPU or the rest of the system? What's the safe way to proceed here? I tried a google search but didn't find anything helpful, so if anyone knows the score I'd be pretty grateful.

Since cores "in the field" - that is, once they leave the factory - are locked and unlocked via the motherboard board BIOS (IF and only if the motherboard's BIOS Setup Menu supports that feature), I would look at your motherboard. You might check to see if there is a new BIOS update that addresses this issue.

As far as I have found, no harm is done if you unlock it again.

Thanks. I re-enabled it and ran a quick test with Prime95 and all seems well. Still not sure what tripped it off, but I'll be keeping an eye on it to see if it happens again.