Try going directly to this URL:
https://wheelheads.riverroaring.com/login?safe_mode=no_themes,no_plugins
The normal method of entering safe-mode seems to be broken on your site.
I think you will be able to login from that URL. Once you have logged in, go to your Admin / Customize page, enable the Default Discourse theme and remove all theme components from that theme. If that works, you can then try to figure out what is causing the issue. I’m guessing it’s your site’s theme, or a theme component.