Arduino Uno pin dead for no reason. Why?
I have quite a few Arduinos lying around and only one has failed completely, which I think is because I "zapped" it with static electricity, which is a problem, as Chris Stratton suggested.

Make a habit of grounding yourself before handling electronics, for example by touching some metal (earthed) part before reaching for your Arduino. Don't work while standing on a synthetic carpet, for example.


  but what causes my pin 5 to be dead?


Possible reasons:


static electricity
accidentally shorted an output pin to ground, which could damage the output driver if you are outputting HIGH
accidentally connected an output pin to +5V, which could damage the output driver if you are outputting LOW
connected the pin to a negative voltage
connected the pin to more than +5V
powering the board "parasitically" which means connecting power to the data pins before connecting power to the main power input
tried to "sink or source" more than 40 mA which is the absolute maximum rating. For example, connecting an LED directly to the pin without a current-limiting resistor




The other link he refers to: Bad LCD? Bad microcontroller? Or what?