The method to burn Bootloader to the Arduino Board
When you have chosen the right board and port, and there is no connection between TX/RX and the circuit. If you still fail to deliver the code, the bootloader of your board may have lost, then you need to re-burn the bootloader to your board. Just take how to burn it to UNO as an example, there are two ways, if you already have one USBtinyUSP, the burning will be much easier, if you don’t have one, you can use UNO or Duemilanove as the programmer.
Method 1 Use USBTinyUSP as the Programmer
1.Open the Arduino IDE and choose your board type. What should be burnt here is UNO, so choose UNO.
2.Choose Programmer USBTinyISP here
3.Click Burn Bootloader
4.Wait for a while and if there appears Done Burning bootloader in IDE. It indicates that you have uploaded the bootloader successfully.
Method2 Use Uno or Duemilanove as the programmer
Attention: After testing, this kind of method just used successfully in Arduino Duemilanove, arduino nano, arduino uno who use 328P.
2 Arduino Board( One as the Prammer and one need to burn bootloader)
Upload code to Programmer
1)Open the Arduino IDE and choose your board type. What should be burnt here is UNO, so choose UNO. 2)Choose Programmer Arduino as ISP here. 3)Click Burn Bootloader
For details, please refer to https://www.arduino.cc/en/Tutorial/ArduinoISP