S-Video hook up to TV

I just got a desktop computer from a friend with Linux on it and I'm completely unfamiliar with the system, but I haven't gotten a chance to try it yet because I was planning to have my monitor be my television screen. My television, however, only has three plug ins: DVI, AV, and S-Video. The computer came with an extra video chip that has an S-Video output on it. So, I tried plugging the S-video from the computer to the TV. I turned it on. While in DOS, the screen was fine. But, as soon as the Linux system started up, the screen started flashing up and down. Like this, it is completely impossible to work on it. I need to know if there is a Linux setting to adjust the video output so that this doesn't happen. I can borrow a monitor to set it up correctly, but I need to know how.