What does four flashing red lights on the xbox 360 mean

Power off
take all you have connected to your xbox out unplug everything then take out the harddrive and then connect it all back together it fixes the problem all the time i get that. If not then you can talk to their support at xbox.com/support but it does have to do with your mother board it can be reset by unpluging it all and taking out harddrive.

If it doesnt come on and you have 3 lights flashing you have red light of death

what happend was you xbox overheated and it melted the CPU chip on your board, well didnt melt the chip but the solder around it there for it made soldering bridge connecting by melting 2 different component slots of solder into 1 so you will have to take it apart and resolder it. Or you can send it to Microsoft and they can fix it for ya for some $$$ out of your pocket but mostly they just give you new one and you loose all you data and saves so i did mine my self.

You tube has guy named gilski he shows how to fix ps3 and xbox red and yellow lights of death