I have the same problem with my HP Pavilion dv4 1225dx, at the begining it was a green horizontal line on the botton of the screen now it has expanded and covering all the taskbar.
I chat with an HP tech support and says it is a hardware problem and it will cost me $398 plus taxes to fix it. He recomend me to buy another computer.
It looks like this is a common problem with this laptop, there should be a recall or something. HP mess up and want us to pay for this mistake?... I don't think so.
If I can't find an esasy fix with this computer. I will file a complain with the Federal Trade Comision. Nevermind, I am going to file a complain now, I hope the people who is having this same problem do the same.
here is the link