It can also releadted to the install of the DNN while the permissions on the server are not setting right. Some Hosting Software have some restrictions to setting permissions. I have some knowledge on Plesk. Also some wrong or missing settings can caused issues on installation if they missed in the web.config file.
Some 3rd parity skins used own controls, and it can be they changed the core controls or added some controles. On not well coding it can be that there is no way back or uninstall that controls.
On the Link you have posted, I sawed a 3rd parity skin.
To help you, I need more information about the permissions on installing DNN of the DNN paths and the IIS and the configuring of the SQL Database. Have you following the install instraction from the Install manuel?
You asking how to reinstall the register Modules. This gives me a other question have you uninstall it? If yes I would say do never uninstall the Login and User Account module! If you whish to use a 3rd parity user account module or login module, then first try it if they work probertly.