Yesterday evening when i was mindlessly streaming on my ipad, it accidently slipped and landed on my computer case where it immediately lost power and shut off. I tried turning it back on and it did, although there was apparently no signal to the monitor. I use a VGA cable and i tried plugging it into the mobo aswell as my gfx card. I also tried using a hdmi cable but still had no signal. Another point worth mentioning is that the lights on all my devices such as my mouse and wireless usb adapter were significantly dimmer.
Motherboard or power supply, open the case and reseat the connections and also reset the BIOS to defaults. Then try again. If there is power but no video signal, that points to motherboard of power supply most of the time. RAM, video card or CPU would have beep codes most of the times if those were bad.