Hooked up Apple TV; screen filled with colorful static.

I'm trying to hook my Apple TV up for the very first time (to a Roku smart TV, about 2 or 3 years old). When I switch to the HDMI1 port, where it's hooked up, I can make out the setup screens, barely, but the entire screen is covered with colorful static (see picture).

I tried a different HDMI cable -- same thing. I tried the other HDMI port on my TV, but it didn't recognize it at all.

Any suggestions?