Cannot upload application to a UNO-board from Mac Pro

Using Arduino Installation & Troubleshooting
#1

I have a UNO board and a Mac with OS X version 10.5.8 the does not work together. I know that the board works OK, since I have tested it with a Windows 7 computer. I simply cannot get it to work my Mac, hate to buy a new computer (with Windows 7) just get started on my project.

I get the following error from Arduino IDE when trying to upload the "Blink" application:
avrdude: Version 5.11, compiled on Sep 2 2011 at 18:52:52
Copyright (c) 2000-2005 Brian Dean, http://www.bdmicro.com/
Copyright (c) 2007-2009 Joerg Wunsch

System wide configuration file is "/Applications/arduino_1.0.4/Arduino.app/Contents/Resources/Java/hardware/tools/avr/etc/avrdude.conf"
User configuration file is "/Users/ornstein/.avrduderc"
User configuration file does not exist or is not a regular file, skipping

Using Port : /dev/tty.usbmodem1a21
Using Programmer : arduino
Overriding Baud Rate : 115200
avrdude: Send: 0 [30] [20]
avrdude: Send: 0 [30] [20]
avrdude: Send: 0 [30] [20]
avrdude: ser_recv(): programmer is not responding
avrdude: stk500_recv(): programmer is not responding

I have read the instructions thoroughly and done everything they tell me to do. Please help me!!!!

#2

Bad USB cable or port?
Have you tried the loopback test (stickied) to see if round-trip communications is possible.
Do the Receive and Transmit lights on the Arduino blink when you try the upload?

#3

I used the same cable when uploading to the same board from The Windows computer. So this leaves me with a possible faulty port? Have ruled out this possibilty since I can use the port for other puposes like connecting a RaspberryPi. I can however not see the leds blink when trying to uploading.
Will try the loopback test.

#4