Have you tried the answers mentioned in this thread?
And, when your iPad is connected to iTunes (via the USB cord) - are you saying that a right click on the iPad line (in the left column) does not give you a pop-up where you can select the option to Backup?
In other words, what specifically is, or is not happening? Are you getting an error notice? Or is nothing happening?
Answering these questions will help us help you to narrow down your issue so that we can hopefully help you.