I have a HP presaro V3000 with the same problem. The laptop is 18 months old. Within the first 6 months the mother board was replaced. At 12 months old it had the same problem again but I was told there was nothing wrong with it. I got it home from HP service & it would still not come to life. I took it back & was told it was now out of warranty. After much arguement with HP they replaced the mother board for the second time. I have just had the problem again & have taken it to a laptop repairer here in Australia who told me this is an ongoing problem with HP. He refloated the solder on the mother & told me I may get another few months out of the laptop. I am now back to having to try & reboot boot two or three times before the screen comes to life.
This is the worst lap top I have ever owned. Never again a HP.