I follow the older posts but I couldn't fix the problem.
I created a hex file with the firmware of the ATmega8U2 from a working arduino and uploaded in the not working one but it returns me always the same error:
avrdude: stk500_getsync(): not in sync: resp=0x00
avrdude: stk500_disable(): protocol error, expect=0x14, resp=0x51
thank's a lot.
have the right board selected?
any other USB devices plugged into the computer?
any other USB drivers installed?
The board is correct: arduino uno
if I use another Arduino uno (I have 6 boards), it works.
I use windows XP as operating system.
I saw another issue similar to this where the drivers for another USB device thought the Arduino was another device and therefore messed around with Serial communications. Look around for other drivers, but I don't have a PC... sorry.