For those with the same issue, could you please check whether the following alternative procedure found by simonsimons34 works for you?
- Hold the the following keys at boot time: Esc+Menu+Minus
- This brings the diagnostics menu. Then run the NAND tests (I don't know which option it is)
- Exit the diags software. The OS will hopefully boot normally.
I just would like to thank you as this worked for me when my calc was stuck after I had to reset it running Linux since it wouldn't close.