How to find if my motherboard is dead

I dis-assemble hundreds of Nexus 7s every month and sell the parts. To be sure your MB is dead 1st you need to make sure your connections are all good. If you know your battery isn't "bricked" that is also important. If they sit for too long without use they will become so dead they can't be charged with a USB cable or other conventional methods. People often mis-diagnose one or the other. If it has been taken apart and you press power and see nothing on the screen it doesn't mean it didn't power up. The LCD or LCD cable could be the issue. To rule this out I often will plug them into a PC that has fastboot and ADB drivers installed. Fastboot would be more important here. I would hold power for at least 30 seconds and watch your PC and listen for a device connecting. Often when they are "dead" they will still show something is connected. Either it will say "device not recognized" or possibly (APX device). If you are sure your connections are good then that almost always means it is bad. If you hear connecting and disconnecting try holding power until it disconnects and power and volume down. Once in a while when they won't boot they will sometimes boot into fastboot mode. I've brought a few back from the dead by doing that.

Hope that helps.