Cable Caniptions

I have been using the converter cable with my PB Pro SH and SSDC for 3 years with no problems. Last week I unplugged the cable to use on another track - using the same computer. Day 1 was fine, but from day 2 I was unable to access race start, pause etc or see any drivers/laptimes/fuel use etc on SSDC screen. Replugged into original PB and same result. The cable is being recognised as COM4 but doesn't seem to be transferring any data. Any ideas appreciated.