I've followed this thread. After hearing that the OP delved into the Registry and deleted files...reformat it.
I like to think of myself as pretty techy, but even I don't screw with the Registry without first creating a backup on a thumb drive. Also, as ReMark said, always make a System Restore Point before installing software.
Reformat the computer. Yeah, you'll have downtime while backing up files and doing the reformat, but it will save you a lot of "hunt and destroy" headache.
There's no reason your computer shouldn't run Revit Arch 2012, my Dell XPS M1330 runs it just fine (wish I had a better GPU, though). I think you missed something in the install, then botched the uninstall. It takes a while; it may look like it's doing nothing, but just let it sit.