I have an HP Pavilion dv4 Laptop where the screen suddenly went blank. I connected an external monitor and both screens had video. I disconnected the external monitor and the laptop lcd stayed on until I rebooted. The I was back to a blank screen again. Sometime it will work with the external monitor and sometimes is won't but when it does both the external and the lcd will work. I have checked the RAM and it is good. When I have had the system running I checked the power settings and they are normal. Any suggestions as to what might be failing on this laptop?