I have upgraded my computer for gaming and i had vista on my old hard drive. I had to reinstall vista onto another hard drive and it said that my serial code was in use. I have no clue what to do. Please help!

call microsoft and tell them you had a hard drive failure and they will give you a working code, that is if you can prove that you own the original copy

You didn't have to reinstall vista in the first place just mirror your old hard drive to the new one, thats what I did. You just copy the old hard drive onto the new one using software that came with new harddrive or that you can download from maker of harddrive. It might ask you to reactivate Vista though it because of hardware changes. No biggie though.