password

I am unable to access Linux mint because it no longer accepts the password. It does not come back with an error (invalid) so what I input is correct but Linux does not start up. I cannot get into anything to fix the problem, I am having to use windows to send this message, thankfully I have retained a dual boot option.
Advise on this problem would be most welcome, thanks

At the login screen hit Ctrl+Alt+F2, are you able to log on in text mode ?

If you run:

df -h

are any of the partitions full ?

If you can log on in text mode, do you get any error if you run:

sudo service lightdm restart