I have a Compaq Presario r4000 that was dropped. Since then , there are vertical bars on the right side of the screen. I changed the screen, but that didn't solve my problem. Someone told me this is obviously a graphics card problem. Can I replace the graphics card on this?
If you replaced the screen, that rules out the screen (well, it still could be the screen, it just makes it many times less likely). The only other thing related to video is your motherboard. In that regard, I would take the unit apart and make sure no heatsink got bumped around and is making it thermally unsound. I really doubt that will fix anything...but it doesn't cost a dime and it's worth a try.
Else, your motherboard is bad. Since you've an X200 GPU, that's integrated into your motherboard - which is what leads me to believe that's your issue.