Need more info.
Brand and model of thumb drives?
How were the drives originally formatted?
Specific version of Windows and service pack on the computer that's not working?
Versions of Windows (or other OSes) you successfully tested the drives on?
Without that information, the only thing I could recommend trying at this point is taking the drive to a computer the drives work on, copying everything off, then taking it back to the problematic computer and letting it format. Then take it back to the original computer, copy the files back on, then try again.