Couldn't upload sketch to arduino nano

I couldn't upload my program to my arduino nano V3.0. I don't know what happened. I was still working perfectly an hour ago. The serial port is correct. I choose the right board. I choose 'arduino as isp' in the programmer section. The nano works fine. I can still see output on the serial monitor of the last program I uploaded. The error message was "avrdude: stk500_getsync(): not in sync: resp=0xe0". When uploading, the RX light and the TX light are both blinking. Is there any possible that the arduino board was destoryed so that I couldn't upload sketch? because I accidently switched the positive and negative power input of 7.4 v on the 5v pin and I heard something weird from the board and then I unpluged it immediately. After this, it became wild. I don't know to much about arduino, so please help me, I don't want to lose my board.

Hello!!

“avrdude: stk500_getsync(): not in sync: resp=0xe0”

you may choosen correct board on arduino IDE.
choose the correct board from Tools->Board->

Is there any possible that the arduino board was destoryed so that I couldn't upload sketch? because I accidently switched the positive and negative power input of 7.4 v on the 5v pin and I heard something weird from the board and then I unpluged it immediately.

That may have wrecked the board. Try this: connect Reset pin to GND, then the Loopback Test. If that fails, the USB/Serial interface is dead, so you won't be able to upload. If it passes, yet you cannot upload programs, the '328P chip is dead. If either chip gets hot to the touch when the power is turned on, the chip is dead. Since the board is all surface mount, you are pretty much out of luck if replacement is needed. Get an FTDI Basic and a Promini for your next round of testing until you more proficient making connections.

Thanks for your reply! How do I know if it passes or not? If the chip is dead, why is the board still able to run my last program? Oh, and I also just found out that if I changed the baud number. It gave me some wierd stuff, no matter I typed in something or not, it showed a bunch of characters that i didn't understand. Does it mean that the board has been broken?

  1. Connect the terminal application to the serial port for your board. The baud rate is irrelevant.

  2. Send data by typing. Everything you type should be echoed back. To send data, some terminal applications, like Serial Monitor, require pressing the Enter key or clicking a Send button. If exactly what you send is echoed back then the board passes the test. This means that the host computer hardware driver, USB cable, and USB to serial converter are all working.

Does that work or not? If not, try a different USB cable. Still no go? Then likely the USB/Serial adapter chip got fried, and the '328P may be ok.