No! Stop right there. Reinstalling is a terrible instinct (in all cases, not just Virtualmin). It can’t fix anything and is very likely to break other things.
OK, I’m understanding that you cannot login to Virtualmin/Webmin? I assume you’re trying to connect on port 10000? (It isn’t indicated in the error above, so I assumed you were talking about your website(s), rather than Virtualmin/Webmin.)
If so, make sure Webmin is running:
systemctl status webmin
If it isn’t, you’ll want to look in /var/webmin/miniserv.error for clues about why, and maybe also the journal (journalctl -fu webmin).