Thanks for the replies, muungwana and Texstar.
I am running 18.104.22.168; I lost connection while taking an overload of classes/working and since it was a spare computer (at least it was then!) I left it until summer to fix. I ran the diagnostics suggested on the sticky thread from this forum, aka the same ones suggested by you, muung, before I asked for help. It came back with green OKs until that driver was listed.
I tried updating to the current kernel, but even the cable-in method isn't functioning. It's an internal piece of hardware and it was built by an expert. I know I was mildly tinkering with things when I lost the connection, but since it was several months ago I don't remember any details.
I've backed up everything I care about; would simply reinstalling the OS fix my issue? Or would the driver still be a problem even with a fresh OS?