We used an external power supply (DC plug) with 8V. After some time all the lights went off. We immediately removed the DC plug. Since then as soon as we plug in a 5V pin, the arduino shuts down. Whats wrong?

Have I overcooked my arduino?

arrrrrduino September 30, 2016, 3:28pm 3

I mean a 5V output, while powered by USB. I can upload sketches, but the 5V output doesnt work.
I work with an official arduino mega.

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