I bought my computer about three years ago which came pre-installed with Windows XP, but included a Vista Home Premium Upgrade. When the Upgrade finally came, I successfully installed and activated Home Premium, and my computer remained for over two years like this - perfectly working. However, recently I had to reinstall the operating system, but I had since lost my Home Premium product key. So I skipped the activation, and was given thirty days until the copy I had installed would operate with reduced functionality. During this time, I tried to find my product key by running programs such as Keyfinder. I would then attempt to activate Vista by entering the key given to me by the program. This did not work, and I got the following for the error:

Code: 0xC004C003

Description: The activation server determined the specified product key is in use.

Now, the thirty days has passed, and a can only use my computer in reduced functionality mode, being limited completely to the internet. I believe that my product key was thrown out accidentally, so now I don't know at all what to do. It suggests that I buy another product key, but I've already purchased one. Any help is greatly appreciated.