Be certain that the proper ports are open for that one site. Also make sure that there is no firewall turned on on the remote PC.
Your question isn’t really clear. You can ping to the IP address, but you can’t UNC into the machine?
If that’s the case, turn on file and printer sharing and add the exception to the firewall or turn the firewall off completely.
If it is an issue with the entire site, you need to open the SBM (TCP 445) port on the local and remote network firewalls.