Won't turn on unless plugged to mains

My Acer N300 is fully charged (permanent green light) but everytime I move it from the mains cradle, the blue light comes on permanently (bluetooth is turned off), the screen buzzes as if 'online' and then turns off. I then can't turn it on again unless I plug it in again to the mains. When I do plug it in again, it seems to do a soft reset each time. I use the PDA purely for my diary, address book and notes so don't have any need for bluetooth, wireless or anything like that.