c140-computer will not recognise unit

We have a c140. It has been a great unit, but now the computer does not recognize it.  We also have an m240.  Today the computer did not recognize it either.  But I put the unit on hold, plugged it in, held the center button for 5-7 seconds and it reconized it.  When I tried that with the c140, it did not recognize it.  We have had it a couple of years, and no longer have any software that came with it.  Using a Dell Dimension 2400 computer with Win XP and WMP 10.  Anyone know of a fix?  TIA

Message Edited by bcarr123 on 08-13-2008 01:08 PM