It usually does this shortly after POST. It has done this while I was in the bios screen also. After the machine sits idle 24+ hours, it may have video for 60 seconds or longer. The longer it sits, the longer it has video, and the longer it takes to go from lines to backlight only. I was addressing a malware issue of random shut offs here when this issue began (nothing was resolved because of the video issue). The machine first started shutting off (like I pulled the plug) before the horizontal line issue began (usually while running a virus scan). If I keep attempting to reboot, it will eventually go straight to backlight only when powered on.
My machine is a HP Pavilion G7-1070us 2.53GHz Intel Core i3-380M Processor with 4 gigs of ram and Intel HD Graphics - Win 7 SP1 for the OS.
I don't know much about the insides of a laptop, but could tear down (and put back together!) a tower, no problem... for what its worth.
I hope someone can help save me... I like this machine!