random lock ups

ever since i installed my dvd rom drive my computer randomly locks up a few times a day and requires me to hit it in the side to work again. however, if i don't hit it within 20 seconds then it will blue screen when I hit it. I can only hit it within 20 seconds unless I want to lose all my work.

basically, how do i fix this?

i've had it for ages though, i've just lived with it and assumed it was meant to do it