Pavillion DV6 oscillates on start up can't select operating system

Pavillion DV6 7010us on start up the screen is oscillating, it states to select an operating to start but can't as it is oscillating, running Windows 7,  if I power up and down the laptop sometimes it will boot up correctly and then I can use it for awhile, but then will start to oscillate again and it can't be used, no key strokes will work