You can try to unlock you X3 720 by a bios setting called "Advanced Clock calibration"
Set it "Per Core" With a setting of "-2" per individual core. If that doesn't work try "0" and try again.
Play with the settings. And torture test with Prime95 for stability.
If you can get it to work stable you are a lucky man. Mine unlocked but failed the stability test @ default speed.
If it won't even boot you core Is probably defective as such and you will have to set your setting back to disabled to reset. I unlocked mine with a MA790FXT-UD5P. With the F2 according to Gigabites Bios info for you mobo it should be possible to unlock your core, but I am not aware of any reports regarding attempts with your board.
The X3 720 is a great overclocker with setting "Advanced Clock calibration" to disabled. And is a fine processor for it's price.
With the F2 according to Gigabites Bios info for you mobo it should be possible to unlock your core.