Satelite m115 s3094 will not work on AC ada...

Hi,

a year ago or so me and my brother got a m115 s3094 each, and a month ago my brothers laptop wont charge. at first we thought it was the ac adapter, so we tried on mines, and it was working. then we switch the batteries in case it was the battery, and the battery is fine, i was able to charge it with my laptop using his battery and ac adapter. We connected and it wont charge, but it will turn on with a full charge battery. So how can we fix the ac plug on the laptop and how much can it cost?