You are very unfortunate that your WinXP computer does not recognize your Dingoo. It must be a hardware problem then. I take it that your Dingo used to connect just fine? Then it may be any of the following: the cable, your PC or the Dingoo. Have you dropped your Dingoo or something like that?
If you still have any warranty left I'd contact your retailer if I were you. Your Dingoo may be broke. I'm sorry...