hi
had same issue. i think likely cause is the power board/digitizer board. i had a n7 2nd gen which was given to me. battery was flat and it would not charge. i replaced board with known working board and when i connected power and tired to power in it flashed 5 times white. left it for 5 mins and then tried again and now it powers screen on and shows batt sign. so to recap
* if your n7 was working (day before) and just stops then its the power board
* get a volt meter and check battery has a charge, no charge after being plugged in then poss dead batt
* if your n7 has been off for a long time, then leave it 5-10 min then try again, if still happening then swap power board and then leave to charge and power on
hope that helps, they are good little tablets to work on, just a shame you have to work on them so often and the parts are getting more and more expensive