And just so you know, if you have an S-video cable, it's the yellow A/V cable you unhook; the red and white ones are for the sound. If you leave the yellow one hooked in and unplug the other two, you'll have two video sources and no sound.
Remotes usually have a button on them that says "tv/video," "source," or (common for Thomson Consumer Electronics products such as yours), "input," or something along those lines. Do you still have the remote that actually came with the TV? GE/RCA TVs usually have a remote like this:
...or like this:
The input button should do the trick. Make sure you turn on the DVD player first, so that it's sending an image to the TV when it gets selected so you know you've selected it.