No charging symbol shown

I never had problems with my charger since i bought my mobile. Its nearly been 1 and half year since i bought the mobile. Today morning i plugged in my charger where it did not even show the charging symbol nor the led light but the light on the adapter was on. After an hour i tried it plugging into different socket. At that time i found the adapter's light was still on though i plugged it out of the socket. I dint know what the problem is. Then I rebooted my mobile where i found the charge to have increased from 4% to 50%. What is the problem here?