The product key code that was given to me doesn't work

So just now, my pc wouldn't Windows 7 Keygenboot, and none of the repairing stuff would work (system restore, using the win7 disc and doing startup repair) none of it was able to make my machiene boot. so inevitably i reinstalled Buy Office 2010 from microsoft. how can i get my key back? i really don't want to have that money go down the toilet. how would i be able to get Office Ultimate 2007 Key it back or get another one?