I downloaded the Nero 126.96.36.199 from our website, chose the 'Custom Install' and enabled InCD 5 to be installed along with all the other components.
Then rebooted and InCD was in the 'Taskbar' and would launch and allow me to format and write to a DVD+RW disc without asking for a serial key.
You only need the one serial key to intsall all of the Nero 7 components.
I would recommend uninstalling using the Nero Clean Tool, and then a fresh install and see if this resolves your issue.
If not, then send me an Email at Techsupport4@nero.com
and in the Email detail your isssues or provide a link to this thread, and include your Serial key so that I can test and see if there is an issue with your serial key.