Trying to install on Windows 7. I get the message: "The key "[my product key here]" is not valid. Verify that you entered the correct key." I'm typing the exact key from the DVD envelope. I may have installed this a few years ago on same computer when it had XP on it, (can't remember), but I wiped the computer clean when I upgraded to 64-bit Windows 7. I suspect this may be the problem. Can I still use the key or somehow get one that works?