When i connect arduino at the usb port, the tx light is every on, so when i try to upload a rpogram it says that the board doesn't respond.....Help me !!
If you are running Windows I would re-install the drivers for the FTDI usb-to-serial chip.
If that doesn't work then I would make the parallel programmer cable and try reloading the boot loader.
After that I might think that the FTDI chip is bad.