Problem with video on my computer?

My parents asked me to fix their computer. Turned out to be a nightmare, but now I've got it running smoothly. The only thing I'm not able to figure out or fix is that there seems to be a problem with anything that may need to use the graphics card at all. Youtube videos will freeze with the audio playing without a problem. Flash games, downloaded videos, DVDs, etc do the exact same. Now, there's no problem with the audio. It'll play smoothly whether the video freezes or the frame rate slows ridiculously, which leads me to believe it's solely a problem with the graphics card. My parents have had this computer for four years, and they say it has been doing this for about two. Is the problem the graphics card and is there any possible way to fix this?