login password

Is you account locked (many distributions added brute-force protection in the PAM configuration for logons)?

Check this using the pam_tally2 command (sudo and --help for details, or the man pages) and use the pam_tally2 --unlock command to allow your account access again.

If the /etc/pam.d/system-login contains the lockout and the tallylog is not present in the /var/log/ directory, create it. (usually after 3-5 attempts and if you try again. within 600s, it will not unlock automatically, and well, it is not a uncommon issue).

Ty bypass passwords entirely, use your bootloader, hold shift if required to interrupt the start of GRUB, press 'e', a long line of jibberish (the kernel command line will show up), add 'init=/bin/sh' and press enter to start your system as the root user (this is a BAD solution).
You should now have bypassed any password restriction and be logged on as the root user (which you really never should use).

The best solution to gain access:
Chroot in to the system, mount the partitions, make the required repairs and then add a password to the bootloader to restrict it from allowing anyone to logon locally

A system is not broken until the hardware has died and can always be fixed.