either you deleted your admin user instead of changing the password, or someone else deleted the users table, or you never had anything in it at all.
If you never had anything in it at all, it would be because your installation failed. In this case, it is best to start over and reinstall (as there are likely other problems, and it can take a long time to sort them out, a lot longer than a quick reinstall).
If you deleted your admin user, that would not explain the rest of them being missing.
If someone else deleted your users table ... you have a security issue and will need to resolve that and then reinstall to be sure you have a clean system.
What I am getting at here: If you fear the reinstall, you'll have a miserable time with Vicidial ... but if you reinstall several times and get used to it, you will find that building the Vicidial Server gets easier each time and there will then be nothing to fear. Then you can work on Reading the Manual while making money with Vicidial.
If you do not observe any errors in the vicidial.log resulting from a problem during installation ... you'll need to check the .sql file used during installation for your version (in /usr/src/astguiclient/VERSION) and work backwards from the last command to find which command DID work ... then you may be able to find which command failed and manually execute them from there to the end.
Or try GoAutoDial or 3.1.15 ...
And watch for errors during the install!
Happy Hunting!