Dmkkg,
Since the owner of the remote machine has switched to a different ISP and installed a new router, its a strong possibility that their network configuration has changed. Unless they were able to keep their old IP address and configure port forwarding on the new router the way it was previously, you wouldnt be able to connect using the old information.
Even though the machine still shows up in Windows Explorer, youre not going to be able to connect to it without first getting the new information from the owner of the remote machine.
I hope this helps.
Mike