I just did a simple repair to fix a dv9720us. It was rebooting anywhere between 1 & 30 seconds on start up.
My thought it something was causing it to over heat. When I took apart the laptop and removed the heat sink I saw that the Video chipset did not make a "good" contact with the heatsink. I removed the thermal pad that came on it and placed a penny in between the center of the chip and the copper pad on the heatsink.