Why is my printer not printing?

If the printer control panel says:

Change Paper in MPTray
Tabloid
Transparency

Then you should press the ONLINE button to print

To disable this Media Check feature so it won’t happen again, turn it off in Printing Preferences.

If the printer control panel says:

Ready to Print

Then the IP address may have changed when power it off. See “How do I set the IP Address on my printer?” to set manually.