Thank you Jonbart and Joe.
Jonbart - I guess I didn't look as closely as I should have, the LANDesk Management Agent service was missing. The two accounts were in the right groups.
Joe - I must have uninstalled and re-installed the agent at least 3-4 times, even deleting the directories and registry keys manually but it didn't fix it. This time I used the command prompt, stopping the services as you suggested. I also used the /forceclean option this time (not sure why not before), which I'm thinking probably made the difference.
Anyway, I re-isntalled the agent and all the services are now there and the discovery picks up my PC.
Thank you guys for the help!