To solve the issue, you can try the process below :
Formatting the calculator:
1. Press and hold reset (on the back of the calculator, best with a pen so you have the hands free to press the other buttons), the DOC, ENTER, and EE (next to the letter A) buttons simultaneously.
Then you can release the reset button, keeping the rest of the keys still pressed for around 3 seconds.
When the loading bar is loaded up to half, you will have a message « Waiting …. Install operating system now ».
Then process an update of the calculator : you can follow the process here