Hello every one ..
Recently I have moved my default user from Administrator to standard , then I can’t do any thing (Add\remove\mount) ..
To bring it back to administrator do the following :
Reboot using grub and select an entry for recovery mode (hold shift after rebooting to make grub options appear).
Select the “root” option from the Recovery Menu. From the terminal that opens at the very bottom type:
mount -o remount,rw /
sudo addgroup your-username sudo
Then you can resume the boot by holding control and pressing “d” and select resume from the Recovery Menu.
Thats it
MyCodee 