Reentering serial number in Windows 7

Does anyone know how to install a new serial on a working copy of Windows 7 - I get notified that my software is not genuine but cannot reenter the serial

One easy method is to change the key via the command prompt:

1. Click the Start orb
2. Type cmd and press Shift+Ctrl+Enter to open an elevated command prompt.
3. Type in slmgr.vbs -ipk followed by your new key
4. Type slmgr.vbs -ato to re-activate if necessary.

You will be able to enter a new key when you try to activate Windows.

1. Open Control Panel.
2. Go to System.
3. Click Activate Windows. (In case it is not activated) / Click Change Product Key on the lower half (In case it was previously activated).
4. It will ask for a new Serial key.