Arduino ATmega328P works but board (Uno R3) seems broken This is the first time I'm using my Arduino. It's an Arduino UNO R3. I have two boards. One works, but the other doesn't. I changed the ATmega328P from the broken one to the good one and it works, so I can confirm that the controller works. The issue seems to be in the board. 

When I plug the board it doesn't come up either in Mac or in Windows. The LED blinks and the output pins have voltage, but it seems that it's only getting electricity from the computer, it's like the data channels don't respond. The other board works perfectly both on Windows and Mac.

I checked the logs on the Mac and nothing changes when I plug the board. It's like I'm not plugging anything.

Is there a way to reset the board only? Maybe a component was badly soldered in the factory. I can't use the warranty because I got the board last year and never used it until now.
The R3 uses an ATmega16u2 in place of the FTDI. It is possible that it is not loaded, busted crystal, or it has no local power to it. It is a small SMT.

You could use your good Arduino setup as ICSP programmer to talk to the ICSP of the 16u2 to see it is alive. And if so then program it.