Possibly your battery has been allowed to become flattened to the point where it cannot accept a charge from the wall charger. The best thing to do is to try and trickle charge your tablet. This means rather than charging it via a socket if you have the facilities try charging via the lead connected to a computer or laptop - with the computer or laptop connected to mains power. This can take 8-10 hours. It has been pretty well documented that lithium batteries do not like to be drained fully & it may be that the battery in your tablet has drained so low that it cannot accept a charge from the a/c charger.  After you have charged for several hours if it will still not turn on press the power and volume button at the same time and hold them down together until the screen turns on - this can take a few seconds. We have found this solution works for students who have experienced similar problems.  

If you've tried charging it overnight and this doesn't fix the issue, please raise a support ticket

The charging port is located at the top of the tablet to the left of the centre. The USB power connector will only fit in the correct orientation and shouldn't require much force!