IPhone 3g won't connect to computer or iTunes

I tried connecting my iPhone to my computer today but neither the computer nor the phone show any sign of connection. Phone is 3.1.2. Comp is running windows xp media center, iTunes 9.0.3 (or something like that). I've tried doing a full uninstall and reinstall of the iTunes program package (QuickTime, mobile device support, etc) but to no avail. The phone does charge when connected to the wall charger with the same cable, so it's not the cable. Any ideas?