Cannot upload program to arduino

Hello, I am using Arduino Mega 2560. When I am trying to upload a sketch on it, TX starting flashing and it never finishes upload a sketch. The right board is selected and tight port. I plugged Arduino UNO board and successfully uploaded the same code.

I don't have any error message appear until I press RST button (it's says timeout) and TX is continually flushing. I can't figure out what's a problem.

System: MAC OSX 10.4.11
Arduino v.1.0.1