Only display "I2C Scanner Scanning... "

With GY-521 mpu6050 and mega2560 Like the following problem, my project never moves on since "I2C Scanner Scanning... " .However I think the pin is connected correctly. Is it possible that mega board is broken or other error?

Appreciate your help!

However I think the pin is connected correctly.

Pins. SDA to pin 20, SCL to pin 21, 5V to Vcc, ground to ground.