Well how frustrated you must be.
Gosh I bet ill run into this problum myself soon because I plan on upgrading my video card soon

Well best advice I can give is to try out the digital locker in the control panel.
I beleve you can backup your activations online or something But im not shore how it works becaue I have'nt used it.
I seem to recall someone telling me thay just redownloaded thare activation or something.
Digatal locker stores downloaded payed for software activations or product keys like you bought The software in a store.Sorta like paying ms points for xbl dlc I think. Well good luck figureing it out!