This is a design fault in the Nexus - the battery is not fixed snugly internally and is allowed to slide back and fourth and so the connections get loose.
1) open up the back of the nexus as described in this video:
2) you will probably see that the connectors from the battery (large silver rectangular thing) are not secured.
3) push them back in properly, then place a small piece of card to the left of the battery to stop it sliding.
4) put the back, back on.
5) leave it re-charge for a couple of hours.
6) bingo hey presto it works!