If Vista came preinstalled with your computer, the Key is the number on the computer. If you received a DVD with the computer, the numbers are probably not the same and that is why you cannot validate. What you need to to is activate by phone. Explain your situation and have all available information ready. There should not be a problem Activate Vista by Phone
When you install and you are asked for your key, do not give it and untick the box that says activate as soon as I am online.
Dont worry, it will work out.
You have 30 days to activate from that date.
Vista and Seven are activated in the same manner.