I've been working with my Arduino UNO R3 and an Atmega168-20PU (choosing Arduino Diecimila as board to load the program) because I hace a PCB designed to work with it, so I just use Arduino to load the program in the microcontroller.
Suddenly, when I switched the ATmega to to upload another version of my program, the onboard led dinidn't blink as it used to when it recognized the Atmega, and I can't upload programs anymore. The error I get is the typical sync error: no initial serial response from the ATmega. However, if I swicth the ATmega168 to an ATmega320 (selecting Arduino UNO board this time to upload the program properly) it DOES recognize it, and I can upload any program without problems.
I considered the ATmega being broken, but I bought another one and the issue is still the same.
Any ideas would be helpful. Thanks in advance,