My Mac desktop only boots half way and does nothing

Follow the steps for the screen that it stalls on.

see > If your Mac doesn't start up all the way - Apple Support

You have not offered any information as to whether this started occurring suddenly for no other reason, or whether something has been changed or added, so all I can suggest is the following. Your computer does recognize its operating system but is unable to load it at startup. It has become corrupted. Most likely you will have to reinstall a clean new OS since something has corrupted the current OS.