Are you hearing the external drive spin up? Is it spinning up but you are hearing a click sound? I was having problems with my external and found it was the power supply. Try plugging the external into a different USB port. If that doesn't work then you can try taking the drive out of the external housing and hooking it up inside your computer to see if you can access the drive that way. A lot easer to do with SATA because you do not have to worry about primary and secondary settings.
If you are not comfortable inside computers then you will want to have someone that knows their way around to help you out.