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Video issues get complex fairly quickly, but there are several things you can check and/or try:
Double-check your 'source' choice on the touch screen:
Be sure you've chosen the one you want. Some rooms may have more than one cable choice or another source choice may have been inadvertently touched.
Or - Try another presentation source (AirMedia/wireless presentation, HDMI cable) to see if it is working instead.
Is the 'Hide Image' button active?
It looks like this when it is: 
or like this: 
Switch the adapter:
Some rooms may have more than one USB-C to HDMI adapter provided. Additionally, if you have a Carleton-provided laptop, you were also issued a USB-C hub. Please try one or both of those options. OS and hardware updates to BYO devices can play havoc with adapter interoperability.
Didn't find what you needed? - Submit a classroom issue ticket or call Classroom Support at x5002