If you are unable to log into your Sytist admin and just seems to refresh without it saying that the password is incorrect, then most likely you are out of space on your hosting account (or reached a file count limit). No space to create the session file to get you logged in.
You can check in your hosting control panel with your host on your available space. If you are out, you will need to delete some old content from the file manager in your hosting control panel or have your host add some more space to your account.
If you see large error logs in your file manager (error_log, errors.txt), you can delete those to free up some space.
Another option that might allow you to get logged without increasing the space would be to edit the sy-config.php file that is in the Sytist folder through the file manager in your hosting control panel.
Remove these 2 lines IF you have them and save:
ini_set('session.gc_maxlifetime', 1800);
ini_set('session.save_path', $setup['path']."/sy-phpsessions");
Then try to log into your admin again.
If you are not out of space and have reached a file count limit on your hosting, see this.