I've made a little buzzer system with my Arduino Uno few weeks ago, and it worked fine, until the day that i needed it, when i turned it on, and tested a little on the buzzer and poof, it died, and when i try to upload the blink sketch to see whether the board is still working, the programmer not responding problem showed up.
Prior to that, while I was testing the buzzers, one of the transistors burnt out of nowhere, and then when i did the upload, it failed, so I suspect that it has something to do with the transistor. Can anybody please help me troubleshoot this?
This is the circuit diagram showing how the transistor was connected.
The USB-to-serial converter is not OK. If the board uses an Atmel processor for conversion (like on an Uno) it is possible that reflashing the firmware may resolve the problem.
I've just tried it step by step like how it was written in the guide, but it failed when I do "sudo dfu-programmer erase". It says "no device present".
The only thing left is to try to reflash the firmware using your friend's Mega configured as a "programmer". I may be able to help you until you reach the point of actually reflashing the firmware; the avrdude command to execute. Unless someone else steps in to help, at that point you will be on your own.