Windows vista home basic- help validation on change of hard disk?

Question

I have purchased a system with pre-loaded vista home basic. I had to change the hard disc. After re-loading the system prompted that I had to validate the os.
I get the following error message:
The product key is already in use.

How to overcome the problem without buying new os?

Answer 1

If you are using Windows Vista, you could use the activation steps through phone, where it would give you a series of numbers, once you call up Microsoft on [phone], enter the series of numbers dictated and get the product validated.

Answer 2

Call Microsoft and explain your situation.

They will help you for free.