Hopefully this will clarify some things.
If you see the following image:
That is what I would expect to see if you have done the jailbreak, but now need to do a tethered boot.
To do a tethered boot you plug the power into the ATV and connect it via USB to your PC/Mac. Then start SeasonPass (not iTunes) and use the tethered boot option. Once that has been done you remove the USB cable and plug in the HDMI cable WITHOUT ever disconnecting the power.
If you disconnect the power at all or your power goes out you will need to boot tethered again. It is recommended to use a laptop to boot tethered because you cannot disconnect the power at all.
Image credit henrik343