It sounds like the screw has stripped or the screw bushing has stripped. You can easily check this by looking at the screw itself. If the threads look sound, then take one of the other screws out of your grips and try screwing it in. If that one is loose, too, then the grip screw bushing is stripped out and will have to be replaced. In which case you can send the pistol to Taurus for repair, or you can find a local gunsmith to do the repair. If a local gunsmith can do the work for you at around $50, then that will be the way to go, since shipping costs to Taurus is likely going to be more than that unless you live close to Miami.
If the other grip screw goes in nice and tight, as it should, then you can easily order new grip screws from Brownells and replace them all, which I recommed, since the factory grip screws from Taurus aren't the best.
