Sorry to say, you are likely out of luck. Unlocking an "extra" core or two is always a crap shoot, some CPUs will and some just wont!
Having said that, dont sweat it, the Athlon II X3 will do everything you need without the fourth core active.
I bought myself the X4 620 a few months back, then built my daughter a system with an X2 cpu, and it out runs my X4, man was i bummed, could have saved myself some money on my build if i hadnt been greedy.
And btw, on the right MB these CPU overclock GREAT!
Goodluck with the older bios effort, but i think its in vain
Thanks for the reply, yeah I'm actually very happy with the performance from my x3 440. It runs great without the unlocked core, and combined with my XFX 5770 GPU, I've been able to run Sims 3 and Starcraft 2 beta at maxed graphic settings very comfortably on my Acer 21.5" h213h. I've been hesitating on testing out the older bios because I've heard that it's better to not update the bios if my computer is working fine.