Adafruit_Si7021 question

Hello, I have a si7021 sensor. I make sure all the wires are connected properly. (checked header soldering etc.)
I installed Adafruit_Si7021 library. When I run the example code, it keeps giving me

Si7021 test!
Did not find Si7021 sensor!

I run the I2C_scanner, it gives No I2C devices found.

I read the si7021 specs, supposedly the I2C on this sensor is enabled by default.

does it mean th si7021 is dead? Thanks.

I make sure all the wires are connected properly. (checked header soldering etc.)

and

I run the I2C_scanner, it gives No I2C devices found.

is contradictory. Either the soldering is bad (the chip is tiny and correctly soldering it is not an easy task) or your wiring is not as good as you think. You know that the chip must not be powered with more than 3.6V, don't you? Post a wiring diagram!

What type of Arduino are you connecting this sensor to? Did you buy a breakout board (link?) or did you solder the sensor yourself?

does it mean th si7021 is dead?

It might be if you connected it to 5V.