First you need to reset the BIOS to defaults and then use the PII X 2. You can't set the processor itself to being 4 core unlocked permanently. It's the Mobo which does it.
So basically you need to reset the BIOS to defaults, remove CMOS battery, short jumpers, hit a switch whatever and then try to use the processor. Just boot into the BIOS after that. Don't try to change anything there, update to the latest BIOS and that's it.... your FX6100 should be good to go in that board.