Please help, I've tried everything and read all I can.  My 2012 Nexus 7 tablet will only charge if it is turn off completely.  I love reading books on it but can't because it will not charge while the tablet is on.  I have tried everything I have read on line.  Yes I am using the cables that it came with.  I've tried changing it from MTP to FTP (no luck on either).  I've tried turning it off and seeing that it is charging and then turning it back on - still doesn't work, plugging it into my computer.  NO LUCK WITH ANYTHING!  I see this is a big problem all over the internet but nothing seems to help.
I want to use it on trips, etc. but I need to to charge while using it and it hasn't done that since I got it about a year ago.