Have you tried putting more gas back in? If the gauge suddently starts reading again, then it's probably not a float issue. I would also agree that it takes virtually nothing to move the float/arm assembly, so it is unlikely that is has siezed up somehow. But.... is the inside of your tank rusty? Perhaps the sending unit rusted or something built up on the resistors. Also, it could always be the actual gauge itself. I think filling the tank back to full, checking to see if the needle shows gas again, and then re-checking resistence at the sending unit would give you a better idea what's going on.