My iPad with retina display was very slow to charge and now is I am unable to power on the device even after being on the charger for several days, any suggestions??

I have had my iPad with retina display for a little over a year and after about 6 months I noticed it was charging slow. I have bought several new chargers from apple and still the problem continued. Now about 5 months ago I could not even power it on then suddenly it began to work again, but still charged slowly, unfortunetly now I am unable to charge it again or power it on. When I connect the device to my computer via lightening cord it does not even register a device being plugged into my laptop at all. Does anyone have any suggestions, or knowledge of any kind about this irritating situation. It would be much appreciated.