New power supply...

Ok, just replaced the power supply in my computer (I think the old one was dying), checked all the cables, won't start up fully. The hard drive light stays on and I don't get any video. No beeps from the mobo either.

Original problem was random "partial crashes" where I would lose video and sound, but my tower was still on. Figured that was the power supply, as I was trying to add a second hard drive into a system with a 480W power, 2 CD drives, and an ATI card that needs power.

Press the big red button that says "do not push".

Unplug power from everything but the motherboard. Check that you have all the power connections plugged in that the motherboard needs. Turn it on and see what happens. If the monitor doesn't come on and the keyboard lights don't blink, you may be looking at a dead motherboard.