Since you have a Biostar board, you should only have to set ACC to 'auto' in the BIOS, then reboot.
I was able to unlock my 720 BE on my Biostar mATX board by doing this. Of course you might have to raise your voltage a little (1.45v) to stabilize things, but this is your best bet.
If this doesn't work, chances are you have a (truly) bum core.
