can't upload sketch to arduino

hi guys, very strange problem, i tried uploading a sketch on my arduino using my mac and an error occurred ..

Sketch uses 1,116 bytes (3%) of program storage space. Maximum is 32,256 bytes.
Global variables use 11 bytes (0%) of dynamic memory, leaving 2,037 bytes for local variables. Maximum is 2,048 bytes.
avrdude: stk500_recv(): programmer is not responding
processing.app.debug.RunnerException
    at cc.arduino.packages.uploaders.SerialUploader.uploadUsingPreferences(SerialUploader.java:129)
    at processing.app.Sketch.upload(Sketch.java:1672)
    at processing.app.Sketch.exportApplet(Sketch.java:1578)
    at processing.app.Sketch.exportApplet(Sketch.java:1550)
    at processing.app.Editor$DefaultExportHandler.run(Editor.java:2399)
    at java.lang.Thread.run(Thread.java:695)
Caused by: processing.app.debug.RunnerException: Problem uploading to board.  See http://www.arduino.cc/en/Guide/Troubleshooting#upload for suggestions.
    at cc.arduino.packages.Uploader.executeUploadCommand(Uploader.java:113)
    at cc.arduino.packages.uploaders.SerialUploader.uploadUsingPreferences(SerialUploader.java:127)
    ... 5 more

the arduinos tx and rx lights were blinking while uploading but it failed at the end..any ideas? do i need to install drivers if using mac? thanks!