I have an original model nexus 7 tablet. Worked fine for the first few years then started not coming up after either sleeping it or just leaving it alone. Tried all the button tricks to no avail. Read about the slap the back trick and that worked until it bothered my hand slapping this thing. I finally took the back cover off and noticed there are several tiny connectors that touch the back cover when closed. I used the wife's nail file to clean the connections put it back together and it has worked for the last couple of weeks as new. Not sure if that did it but thought I would throw it out there in case it fixes yours.
Stone