Short answer, take it to any repair center if not Nokia and see if they use some special charger to charge it up. One of main reason I did not buy this is the batter is not replaceable.

I had similar situation with n900, I even left it overnight to charge up but no good. Took it to a local retailer and asked what could possibly be worng and he asked one of his assistants to take it inside their lab and 5 minutes alter it had some charging, so I am guessing that if the battery drains out beyond certain limit then it needs some kind of jump start using a super charger.