arduino uno has never worked

Hi,

first, Im french, so please scuse my bad writing...

Second... I have two arduino UNO, bought together. The first has worked very fine, still working as speed regulator in my car, I'm so happy! but now, I'd like to play with the second for an other project. But serial port does not appear anymore in the tool menu. With the same USB wire, the first is recognized, but not the second. The blink program works onto the second when I plug it, but serial port is not recognized on Windows (whatever the OS is, the arduino board does not work).

I tryed with an oscilloscope to see signal on USB connexion, present on the first, but nothing on the second.

It looks like if the ATmega8U2 was not programed. Power 5V is present on the 8U2, wires on the board OK, conexions OK, no short-circuit on USB circuit...

Does someone think I can use the first arduino board to upload a USB program to the second's ATmega8U2 using ICSP 1 and 2 of both boards? I sent an email to my receller, and hope he will change my board, but if I can repare it, I woold be more happy.

bests thanks for anderstanding,

Cinci.

PS : of course, the second should be in my car and the first still on my desktop as prototyping board, so I cut the ICSP plugs as preparing to install it in y car (softly, I don't think it's why my board never worked...).

Prototype place :

in the car...

Thanks KE7GKP, this speed regulator was my first training project so now, I know how to use timers and interrupts by direct register access, because sketches from internet are not... so compatibles...

I tried DFU mode on the 8U2, but nothing worked or changed. I could also use a mini_usb_adapter to upload programs on my broken arduino board, but if I can reprogram the 8U2, it could be fine and better... But how could I upload the HEX file from ATmel328 to 8U2 with ICSP connectors???

did someone allready done that before?