Im currently having the same problem.For my case, it will charge but the port is loose and the usb has to be bent at an angle towards the screen for it to actually connect. After some research I found this is a very common issue for these tablets.
Try using an old micro usb you dont care for and bend it slightly, then place the tablet on a flat surface of the edge of a table with the screen facing down and plug it in (making sure the charger is bending down towards the screen). Kind of an odd fix but it works for me, although i cannot gaurantee this will work for you because your situation may be different, but it is definately worth a try. As for being dropped, being that these are cheap tablets, they are very durable, so having dropped them probably wouldnt have much to do with it (although I may be wrong).
Hope this helps :)
Look in the charging port if everything ok.