The computer I am trying to register on is not connected to the Internet

There is an extra step involved with activating computers not connected to the internet but yes you can still activate the software on your desktop.

When Invoice2go opens click Register then enter your Order Number and click Next.
Then on the second page of the Registration Wizard Click the "Get Activation Key" Link.
Then click the "request a key by email" link on the next dialog and send us the Activation Information as requested. We will then send you a valid key for this machine.

Doesn't answer your question? Try another Invoice2go Frequently Asked Question.