avrdude: stk500_recv(): programmer is not responding PLEASE HELP SOS

I have a brand new arduino uno board and it has been working fine, now I cannot upload any code and every time i try the error message (avrdude: stk500_recv(): programmer is not responding) pops up. when the board is plugged in the L LED and the ON LED turns on when I download stuff the TX and RX LEDs don nothing. I have tried every thing there is on the trouble shooting guid and none of it works. please suggest something as i am considering buying a new board and chucking the other one away.
PLEASE HELP ME!

brej18:
I have a brand new arduino uno board and it has been working fine, now I cannot upload any code and every time i try the error message (avrdude: stk500_recv(): programmer is not responding) pops up. when the board is plugged in the L LED and the ON LED turns on when I download stuff the TX and RX LEDs don nothing. I have tried every thing there is on the trouble shooting guid and none of it works. please suggest something as i am considering buying a new board and chucking the other one away.
PLEASE HELP ME!

You need to post info about your PC (OS etc) and also what version of the IDE you are using

Craig

stesso problema .... Io uso OSX 10.8.2. ... My first post AIUTO OSX 10.8.2