Your controller should have a button labeled input, click it till you see the video.
It depends on how you have your DVD connected. For my it's HDMI2 because my player is connected using HDMI cables. Just go to each one until your picture shows up. If it doesn't then you may not have it connected properly.
It depends on your video output from your DVD player. If you have a HDMI cable connecting your DVD player to your TV (HDMI is one cable), you need to be on HDMI1, HDMI2, or HDMI3. If your DVD player uses RCA connection (3 cables, red white and yellow), you need to select the "Video" input. You can switch inputs by pressing the "source" button on your TV remote on the upper right of the remote. Hope this helps.