The error was that it was trying to validate the catch files and "The Steam servers where to busy", but that wasn't true. I had deleted the game files (in the Library section) to see if I coud reinstall it, but the same error kept going on.
It would sometimes appear in the downloads section of my library, but I couldn't get the download to start.
Today, I went into my steamapps folder to see if there where any files I could delete, just in case that fixed it. As it turns out I had some corrupt .ncf files that didn't get deleted, so I just deleted them myself. Then right before my eyes, I no longer had any problems with the download in Steam.
This is pretty exciting for me because it had broken in March. It had been one of my favorite games, so I instead started to play Left 4 Dead, which got boring.
tl;dr: Jacksaunt is happy because L4D2 works for him.
