I had tried a command (I do not remember it) with the terminal of Ubuntu, and the computer shut down. Now when I boot it, it says :-
[ 4.562057] ACPI PCC probe failed. [ 4.615205 tpm_tis 00:05: A TPM error (7) occurred attempting to read a pcr value Target filesystem doesn't have requested /sbin/init. No init found. Try passing init= bootargw
Busybox v1.21.1 (ubuntu 1:1.21.0-1ubuntu1) built in shell (ash) Enter 'help' for a list of built-in commands.