I finally got my new computer running, and decided to install Empire. I had it installed on my old computer, but it didn't run very well, so I uninstalled it. I'm using the same steam account on my new pc as on my old one, but it still tells me the cd key is a duplicate and can't be used because it's already been activated by my account. So am I just stuck with a useless game that I can't play or even sell, or is there something I can do?

What, so you you registered Empire to your Steam account on your old PC, and you logged into the same Steam account and the CD key is "invalid"?

Download the files via Steam and start it then.

You make sure to have "All Games" selected in the Steam library, then click on the grey entry for Empire and choose Install.

Ah SecurSteam the greatest DRM on earth. No problems with Steam. Hey if steam wasn't required you could just install the game without some over rated DRM getting in the way. Another reason to not buy Steam Games...