I have an hp pavilion a705w. I recently disassembled it to get some dust off and such. I plug all power supply cables back into their designated part, then turn on the computer. The computer sounds like it is running, but no video is displayed. The monitor is plugged in to the computer AND has power. The heat sink fan (which is connected to the motherboard) is active and so is the rear fan, but no video is displayed. The monitor works with the other computers in my house, so I'm thinking my motherboard is bad or damaged. I also plugged in a keyboard to test if the other ports were malfunctioning as well, and the keyboard's lights flashed, but then when I pressed caps/num lock the lights did not turn on. Could my motherboard be broken even if the heat sink is getting power? I'm completely stumped. Some help would be greatly appreciated! Thanks.
It's probably the motherboard, but I would reseat the ram. Unseated ram is the biggest mistake people tend to make if they don't assemble systems often. Use just one stick at a time in case one is bad.