Missing/Un-Downloadable Games?

Greetings.

Many years ago, I purchased Galactic Civilizations. I eventually registered this game on Impulse a few years later. Some time later still, I purchased Sins of a Solar Empire and both of its first two expansions, again on Impulse. At some point I switched to a newer, better computer. For about a year, I didn't bother to reinstall any of these games as I was quite busy with other things at the time, but when I finally did try I discovered that Impulse was gone and had been taken over by Gamestop. Although I managed to eventually get back into my account, the Gamestop application had significant trouble installing SoSE despite the 'efforts' of their support staff. Eventually I just bought Rebellion on steam when it was released, but I'm still unable to access the other games.

More importantly to me, however, my copy of Galactic Civilizations is no longer listed in the Gamestop application. I don't know what happened to it, and I've tried (extensively) to work with their 'support staff' to either get my game back or to get another copy, all to no avail. I lost my physical disc a long time ago, but upon logging onto this website recently to begin a renewed effort, I find a copy of Galactic Civilizations, complete with CD key, listed under "My Downloads." Overjoyed, I thought it would be a simple matter to download it and play again. Instead, both of the "Download" buttons give me a 404 error, and I downloaded Stardock Central in another vain attempt to access my game. Stardock Central does not list my game (although it does list a game I've never ever bought or played?). So, I decided I'd simply just register my CD key with steam (or wherever I could get to take it), but again I had no such luck. I got an 'invalid CD key' error everywhere I took it, and after perusing the help/support boards in depth, I ended up here.

I'm sorry if my post is full of useless information, but I'm tired of dealing with this (and I'm literally tired :P). I just want to play one of my favorite games of all time again. I'd love it if anyone could help me resolve this issue (sometime this year! correspondence with Gamestop would go on for months on end with no real progress). I also still am unable to download and play the original SoSE and its two expansions, but with Rebellion out I don't particularly care to anyway. I'm tempted to just buy GalCiv2 and give it a go, but I'm not in a great financial situation at the moment and even $20 is pretty big stretch.

Thanks in advance to anyone who bothers to read this, let alone help me get my game back.