At the top of this forum are the welcome posts with the generic reset. Try the first reset noted but leave the battery out at first. If that fails, the machine needs repair.
I've had my hp laptop for about a year, I hadn't logged on to it for about 2 weeks. When I next turned it on there was no power at all even when plugged in to the mains. When the over supply is plugged in there is a little white light on the laptop which is on the side where the cable goes in. This light is flashing very quickly. Still no start up tho. Any ideas?