Recently my dad purchased a computer with vista installed on it he has had it for about 3 weeks then all of a sudden yesterday he goes on his computer and it is telling him he needs to enter a product key number so he does that then it goes to another screen telling him to enter a longer product key does anyone know how i can fix this ?

Almost sounds like he deleted some files he shouldn't have, in that case he must call Micrsoft support to get the new number in order to reactivate his copy of Vista.

Yes he must call the Microsoft Support or get in contact with the Computer Vendor to revalidate Vista.

Just for her record... is that Windows Vista copy legal?. That same thing happended to my friend with her computer.

What is going on is that your license of Windows Vista, whichever version it is, was not activated when you bought the computer so you had 30 days to activate it, after that period Windows Vista just stop booting and everytime you turn on the pc you will be asked for the key to activate it. If your copy is legal, and you can check that with the documents delivered to you by the salesman, you should make a phonecall to the number inscribed in the Windows documentation and ask to activate that key, after that you will be supplied (at the exact same phonecall) with that second key which is the activation key. After you fill that key and press activate you should be able to enter Windows and everything should be working properly and your dad's documents should be there too.

So after all it is just a matter of activating the software license, which should have been done before the 30 days limit expired or by the store's staff before the deliver of the computer to your dad.

I hope this will help...