I have an HP envy m6 laptop and recently i've noticed that the display with go black and show a bunch of flashing vertical lines. I replaced the cable maybe six months ago, so I checked that first and it seems ok, although I don't have another one to swap out to see for sure. I made sure all the drivers were updated. The strange thing is, when I plugged it into an external monitor to check if it's the GPU, it showed up fine on the external monitor and the display came back normally on the laptop. Also when I put the laptop to sleep and wake it up, the display comes back normally. I'm at a loss here. Any help would be appreciated.