I am planning on modding a xbox for a friends birthday that is coming up and bought one from goodwill for $10. When I plug it in to power and to the tv and turn it on the green light on the front turns on and I can hear the hard drive spin up and possible the cd drive. However nothing appears on the tv. No sound, No video. If I hit the Eject button the green light flashes but never ejects. If I unplug the av cord it changes from solid green to flashing green and yellow and returns to solid green when I plug it back in. I know the cords and tv are fine as they work with other xboxs.
Any ideas on what might cause this?

http://www.google.ca/search?q=coma+console+xbox

If you try to turn it on about 100x and it works any of those times that's it for sure. (Still could be the issue if it doesn't ever work.) If you can get it to boot you can flash the TSOP and it should fix it. A modchip will also fix it.