Hi @tilly123,
I have downloaded this app and tried to enter troubleshooting mode but nothing happened
On the troubleshooting tab, you can click the button to disable all plugins and change the theme for you while you’re logged in to that session without affecting normal visitors to your site. Note that Health Check may not count Storefront as a default theme, so you can also use Twenty Seventeen as well.
Next, you want to enable only the WooCommerce plugin and see if the login feature is working again.
If that resolves the issue, then one-by-one you can switch back your theme and re-enable your plugins, testing in between, until you find the one causing the conflict.
If you’re not clear about how to proceed, the community team that built the Health Check plugin has provided documentation here to walk you through how to use it – https://make.www.ads-software.com/support/handbook/appendix/troubleshooting-using-the-health-check/.
That should guide you as to what you need to do.