There are two general ways of being locked out of the admin panel: not remembering your password, or having the correct login but still not being able to get in due to some type of error.

If You've Lost Your Password

If you've forgotten your password, go to yoursite/index.php?action=userlogin and enter your administrative account's email address in the lost password form there (if you don't have a valid email address in your profile, edit one in through phpmyadmin first). You should get an email containing a new password to use. This also works if you've forgotten your username, as the email will tell you your username.

If Login is Correct But Still Can't Get In

First, try a login from the front end at yoursite/index.php?action=userlogin. If you can login and use the front end but can't reach the admin panel, you or another admin or some unforseen circumstance must have changed your usergroup to a non-administrative usergroup. You can fix this by finding phpmyadmin in your web hosting control panel, navigating to your yourprefix_members table in phpmyadmin, finding your administrative account in the browse tab, and editing it to set the usergroup to 3.

If the user login page tells you you're logging in, but then redirects to a screen showing you're not logged in, that means you have a cookie problem. This can result from being integrated with another WSN script without matching cookie paths -- if that's the issue, then clear your cookies and override thecookie path and cookie domain with $cookiepath and $cookiedomain lines in tweaks.php on all the integrated sites. Normally the cookiedomain should be .yourdomain.com and cookie path should be /. If not integrated, check your browser settings and whether you can login with a different browser.

If you get a message simply stating that your login is incorrect, try using your email address in place of your username -- you might have selected at Admin -> Settings -> Switches to use emails as logins.

If You Can't Receive Emails

If you're running a localhost testing copy, you may not be able to send emails so can't use the password retrieval. Here's what to do:

1) Register as a new member at your own site through the front end.
2) Use phpmyadmin (it's in most web hosting control panels) to go directly into the database on your server, and manually edit the usergroup for this new member in your wsnlinks_members table to change it to 3. Usergroup 3 is the administrative group. Note: If you require validation of members you'll also need to change the 'validated' field to '1'.
3) Now you can login with the new member's name and edit the password for your original username.

Other Possibilities

Another possibility is that you have recently changed the member system integration setting, in which case you should see the troubleshooting section here and run that query.

Another possibility is that you logged out while in debug mode 'show all queries as executed'. Use phpmyadmin to run this query:

UPDATE wsnlinks_settings SET content="0" WHERE name="debug";

Change wsnlinks_ to your own prefix if applicable.

Notes

The password field in the database is encrypted by default, but if you changed it in the member settings to not encrypt you may be able to read the password from phpmyadmin.