UNO TX doesn't work

It was my first try using arduino.I'm using windows 7 x64, arduino software 1.0, Arduino UNO . When I plugged the board and tried to upload the "Blink" example it gave me an error: avrdude: stk500_getsync(): not in sync: resp=0x00 I tried other cable and another computer(Mac OS this time), errored again (something like the programmer is not responding). Then I tried the loopback test and it failed, only RX light blinks(TX never blinked), and obviously it doesn't echo back anything. What should I do?

I am having the same problem... Did you find a way to fix yours? If so Please let me know.

No, I bought another one, and it haves another problem , it ramdomly freezes and I have to shortcut one of the atmega pins(reset/disconnect doesn't work) =(

Is anything else connected to your board? Are you sure you have the right voltage on your board?

if you are having a problem with 2 of them then it would suggest that there is a problem with your setup.

What board are you running and where did you get it from?

It's connected to my computer via usb, so I think that the voltage is correct(already tried with another computer and external 9V adapter). There are actually 2 LEDs (1 red and 1 infrared) and 1 infrared receiver, I obviously already tried with other projects.

It's an UNO and I got it from MecadoLivre (something like an brazilian ebay)