A very useful tool for determining simple wiring problems (Layer 1) without having to leave your desk is the Time Domain Reflector testing built in to some of the Catalyst switches including the 3750E.

One caveat is that it may cause connectivity problems for the particular tested interface.

Start the test by issuing the command:

Switch#test cable-diagnostics tdr interface gi2/0/2

After a few seconds the test results will be available by issuing this command:

Switch#show cable-diagnostics tdr interface gi2/0/2
TDR test last run on: February 22 10:00:46

Interface Speed Local pair Pair length        Remote pair Pair status
--------- ----- ---------- ------------------ ----------- --------------------
Gi2/0/2   auto  Pair A     N/A                Pair B      Normal
                Pair B     N/A                Pair A      Open
                Pair C     64   +/- 1  meters N/A         Normal
                Pair D     65   +/- 1  meters N/A         Normal

Cisco, Networking 3750, Catalyst, Cisco, IOS