Help Fixing a Friends Computer?!?!

Try installing another OS on it, such as Ubuntu, that pretty much houses drivers for everything. Most network adapters don't generally come with a lot of trouble-shooting tools since they're fairly inexpensive.

Your first option is to swap Operating Systems?? Seems pretty drastic to me. If it was working fine on his Dell before, then maybe a driver update did come out that he hasn't picked up yet. I'd try that first. If not, maybe the cable went bad. Try a different cable.