Ipad 2 apple logo boot loop

So my ipad ran down completely so i plugged it in to charge, and now its stuck in the flashing apple boot loop problem. Ive tried a soft reset, (holding power ans sleep button) no solution.

Ive tried putting it into recovery mode which is where there is a problem, when i plug it into my imac it wont turn it on, it only works when i use a mains plug, so i can get it into recovery mode from there, but then as soon as i take it out of the plug it turns off and im back to square one!

HELP!!