Problem uploading to board [programmer is not responding]

Y'all,

As I was trying to make my BlueTooth shield to work, something went wrong and now Arduino won't even upload the basic blink to the board. I've had this problem before on my desktop computer, and then I would just switch to my laptop to make it work again. But this time it won't.

I've been looking into other topics but I can't seem to fix my problem.

specs:
arduino uno (correct board set)
serial port: tty.usbmodem 621
programmer: USBtinyISP (none of listed programmers seems to make it work)
error: avrdude: stk500_recv(): programmer is not responding

i'm running Mac OSX 10.8.5

I've tried installing USB drivers but this doesn't solve my problem
( http://www.ftdichip.com/Drivers/VCP/MacOSX/FTDIUSBSerialDriver_v2_2_14.dmg )

If someone knows the 'great' solution to this problem i'd be very happy!

Cesar.

Connect a USB cable between the Arduino and PC.

Select Tools->Board->Arduino Uno

Select Tools->Serial Port->tty.usbmodem621

Click on the upload button for the sketch.

What do the RX and TX lights on the UNO do?

Note: The Arduino UNO doesn't use an FTDI chip so the FTDI drivers won't help.