A user reported not be able to access the network. I moved their network cable to another jack and all was well. The 2 wall jacks in question were professional installed Cat 5E cabling, both are plugged into a switch but I can't ping or tracert anything on the network thru them. I applied a cable tester to each end and all the lights sequenced for both jacks. When I put a loopback plug on the user end, connect it to the jack, and then plug the other end of the cable into the switch it lights up. I've tried various patch cables but all the same results.
KNOWN: The computer network configuration is correct. The switch ports are working. The cables in the middle have something wrong.
PROBLEM: How do I isolate what is causing the transmission problem of the cables and how to locate the problem and fix it?