Thank you for contacting Slingbox Forum. I am sorry you are having problems changing the video source on your Slingbox.
In order to change the video source for the Slingbox, you will need to reset the unit to factory settings. This link will give you instructions on how to do it:
You will then need to go to setup.slingbox.com and do the reconfiguration.
Hope this helps with your issue!
Have a great day!
Sling Moderation Team