iPad is not charging???

from one moment to another the iPad of my 8year old isn't charging anymore??

This morning got the message "battery 10%" so I've connected it to the charger and left to do my thing. When checking one hour later the battery is completely drained and I've tried for the past 2 hours to recharge the battery with no luck.

The charger definately is working, I've checked it with my iPhone, so that's not the issue.

Who can help me or had any idea as to what to do since I can't even start the iPad at this moment, eventhough it's connected to the electricity (so no option as to use it while connected to the net)

It's an iPad 1 that we bought from someone else and for the past 3 months no problems at all. At regulare basis charged to 100% and used it to 0% to keep the battery alive. No heat, no sunshine, no water, so al these possible causes are not an option.