Nano v.3 suddenly stopped working (programmer is not responding)

I just got my Arduino Nano v.3 today, which is my first Arduino. I started making simple LED blinking programs just to test it out and everything was working great, i made some small change (i think i changed the delay time of the blinking) and suddenly i couldn’t upload to it. I get the following error message:

avrdude: stk500_recv(): programmer is not responding

The Nano is still working when i plug it in, i can see my code running. It also shows up on my iMac so it is connected, just as it was earlier when it was working. What could be wrong?

Also, and this might be a stupid question but i’m going to ask it anyways, is it possible to upload code that will ruin the device?