Help! My computers breaking itself!?

I have an HP computer that I got a few years ago. What happened last month just happened again.

So I was surfing online last month and I noticed that yellow lines appeared on the LCD screen. it looked like this but yellow and I could still see through the dark spots:

http://www.applefritter.com/files/SE30_screen_garb...

So I thought, ok, I'll turn it off and we'll see what happens. I did it and i could still distinguish those yellow lines when on the vista start-up. The problem was that it just didn't start up again. All it would do is go through the start up procedure a hundred times with a message that says "memory dump". So I returned it for a cleanup and then it worked just like new for a month. It just happened again today. What is going on??? Can I stop this?