Arduino nano stopped working
I suggest you visit the page Have I bricked my Arduino Uno? - whilst you have a Nano and not a Uno, it is the same processor and most of the remarks there will apply.

As the Arduino Nano page says:


  It has more or less the same functionality of the Arduino Duemilanove, but in a different package.


If you have another Uno or similar lying around you could conduct the "chip detector" test described on that page. You could also perform the loopback test.

It is possible on the FTDI chip (underneath) is damaged in which case there would be alternatives to using that.