I am having a confusing error wherein a very basic sketch of Blink an LED performs perfectly when I feed the board with the USB Supply from my laptop. But when I feed the board with 12V 1A Power Adapter, the LED does not blink, it remains ON constantly (and flickers randomly in between). Also, with the power adapter plugged in, the reset button doesn't seem to work.
What could be the possible cause? How to rectify it?