Unable to Change the Product Key

Unable to Change the Product Key
After installing Windows Vista, you may be unable to change the product key to activate Windows.

Cause
Any of the following could contribute to this issue:

The current installation of Windows Vista is not activated.
The new product key is invalid.
You have exceeded the limit of product key changes.
Product key changes for the same activation configuration ID are limited to 10.
Product key changes for different activation configuration IDs are limited to five.
The new product key is for another product (SKU).

Resolution
To resolve this issue, perform the following steps:

If Windows is not activated, follow these steps:
Start Windows, right-click Computer, and then click Properties.
Use normal activation procedures to activate Windows.
If activation fails, use Windows Activation troubleshooting techniques.
Use the troubleshooting techniques in "How to Validate the Product Key."
If the product key change is a product switch, verify the SKU update is valid.
Get the installed SKU by pointing to Start>Run and typing WINVER.
Refer to the product chart to check if it is a step up.