I had similar problem. When i plugged in PDA to my PC, PDA was charging but PC didn't detected hardware. In addition i can't sync my PDA also.

I check connection on two different PC, but i had the same problem.

Is it caused by PDA hardware or Windows bad drivers ?

PC: Windows XP SP 2
Intel 2,8 HT Prescot

PDA: Audiovox PPC4100

Thanks for any advice.