katyro69 , Either the cable or charge port may be damaged. Look in the charge port and blow/pick out(carefully) any dust/debri that may be causing an issue. Try a different compatible charger/cord to see if that is the issue. If different compatible charger/cord does not fix, it is probably a damaged/loose port that will have to be repaired/replaced. This is really not a repair for the inexperienced because the charge port for your device is soldered to the mother board and the heat generated could cause further damage if not very careful. I will post a link to a tear down guide to get you inside the tablet to check the charge port and will also post a link showing what is involved in repairing a mini USB attached to the board. The last link is to new charge port, which you can also do a search for better pricing perhaps. If not wanting to do the repair yourself have a good computer/cell phone repair shop have a look and estimate repair. Good luck.
I hope this helped you out, if so let me know by pressing the helpful button.
[guide|37732]
https://www.youtube.com/watch?v=m-_v-JkNsMg
http://www.ebay.com/itm/Micro-USB-Tablet-Acer-Iconia-A1-A1-830-Charging-Port-Connector-7-9-034-8-0-034-A1311-/400793318953