For MediaTransfer to connect from your iPhone or iPad to your PC, your PC needs to allow it to connect in the first place. Many issues with MediaTransfer are in fact firewall issues. Try turning off Windows Firewall and try MediaTransfer again.
If you use Windows Firewall:
Click here to see how to temporarily turn off Windows Firewall on Windows XP
If this works, the issue is your Firewall... we have some basic help information, but configuration may vary from firewall to firewall.
REMEMBER TO TURN YOUR FIREWALL BACK ON!