If you don’t need any backups, it would be easiest to reinstall the operating system and then a fresh Virtualmin. Otherwise there is a big danger that whatever problem you are seeing now (which you unfortunately did not tell us) persists.
Have you attempted to reset what Virtualmin thinks your MySQL root password is, by going into Webmin -> Servers -> MySQL -> Module Config, and setting “Administration password”?
That would typically resolve that issue.
Also, reinstalling Virtualmin with the install.sh wouldn’t resolve that – but we can certainly toss out some ideas as to how to troubleshoot it.
I agree with Eric that you should check out if Webmin’s MySQL module can access the database okay and fix problems there if there are any. If nothing helps there, it is possible to re-configure mysql (including root account) using your Linux distro’s package manager.