What program/application is asking you for your password? Are you doing something via sudo? or is this some other program?
Do you get any error messages?
If this is related to the use of sudo - Is your user a member of the sudo group?
You can find out by using the following command:
Which will list all of the groups your user is associated with.
If your user IS in the sudo group - then sudo
should work and the only sane explanation is that you have entered your password incorrectly. The only other thing to try might be to change the password for your account, then log out and log back in again.
If your user isn't in the sudo group (i.e. "sudo" is not included in the output from the groups command) - then you will have to log in as another user with root access and then add your user account to the sudo group.
e.g.
Code:
sudo usermod -a -G sudo username
Where username is the user to be added to the sudo group.
I'm not a Mint user, but there's probably also a GUI based user-management application that will allow you to add superuser privileges to your account - assuming that is what you are trying to do.
But before we go too far down the user-management rabbit-hole - I think the first thing to do is get clarification from you about which application is rejecting your password and whether or not your user is a member of the "sudo" group.