Your Arduino Mega is Chinese so it could hapen' that your arduino is not called mega... Let me explain... I bought an Arduino for about 10 weeks ago, and i had the same problem, after researching online a bit i saw that my Arduino Nano is actually called Arduino Micro! But its Nano! So go Tools, Board and try all posible boards, meybe it will work, it worked for me! Hopei helped you and good luck with your problem! Also try uploading you Arduino IDE, cause some Chinese arduinos, for some reason, doesn't work with olds IDE