arduino stop to response - out of sync

hello I'm working with my Arduino Ethernet for a few weeks now today stop working have try to connect the USB Serial to see Serial monitor - don't see nothing Have try to upload a new code (even the simple blink) - got this error

Binary sketch size: 2,494 bytes (of a 32,256 byte maximum) avrdude: stk500_getsync(): not in sync: resp=0x00

the ON LED is just on ,and the Tx LED is blinking when I press reset - I get no response at all

the USB cable is good (I have connect it to another one ) what happened? what can I do to fix it? or even what can I do in order to understand what gone wrong?

Thanks ,

Hold down the Reset button until you get the "Binary sketch size:" message.

this is what I have done : 1. open blink code 2.press and hold reset button 3.upload the code 4. got this error:

Binary sketch size: 2,494 bytes (of a 32,256 byte maximum) avrdude: stk500_getsync(): not in sync: resp=0x00

now what?

Thanks ,