Attempt to repair the Starter install using either a recovery disc and an external disc drive or USB flash drive prepped on another computer with an .iso image of the recovery disc. You may have recieved this as a DVD with your netbook, or alternatively you can get this online if you know where to look. Repair the installation of Starter and then attempt to use the Anytime Upgrade tool with the same key. If you get an error that says the key has already been used, call Microsoft Support and explain the situation. They should be able to deactivate the key for you as well as give you more specific tips than I can.
Best of luck