Was the iPad completely dead or was it just not showing signs of being on? One way to test that it to connect it to iTunes. If iTunes recognizes the device but nothing shows up on the screen, then it could be a backlight or LCD issue.
If the device doesn't react at all, then it could be battery related (first thing to check) or an issue with the logic board or some peripheral that is (camera, sensor etc.) causing issues.
Open up the device, remove the LCD and digitizer (isolate the battery first) and connect it to iTunes to see if the device is recognized. If it's not, you could try a new battery if you have access to one or have it looked at by a micro-solderer.