First, check for loose cable connections inside the case. Then try resetting the bios with the system turned off by removing the motherboard battery for a few seconds, then reinstalling or replacing with a new battery. If it won't power up, try a different power supply. If that doesn't work, then it's time for a board change. Use hp to reinstall your windows setup, unless you have a full installation disk that didn't come with your hp system. Hiper microsystems has an hp socket 939 410895-001 board for $59.99 if yours is 939 and uses ddr pc3200. That's a good price, if they will ship to your location.