[The Comprehensive Kerbal Archive Network (CKAN) Package Manager; v1.18.0 [19 June 2016]]

I would check the cloud config files that are installed when you use CKAN and see if there are textures being used for Kerbin that are not installed. When the Main Menu loads it has Kerbin in the background and will use clouds in this scene. I have had crashes at this point or no clouds rendered when there is a mismatch between what textures there are and what the config files are attempting to load.

Where should I look for that?

[The Comprehensive Kerbal Archive Network (CKAN) Package Manager; v1.18.0 [19 June 2016]]

Are you by any chance getting CTD (Crash To Desktop) without any warning? If so you're probably running out of RAM.

No, I don't. I also don't have this problem if I manually install the Astronomer's Pack. If I install it with CKAN, though, I can't load into the Main Menu.

To clarify, I will load the entire game, all the mods, etc, and when the game actually needs to display anything, it will crash.

[The Comprehensive Kerbal Archive Network (CKAN) Package Manager; v1.18.0 [19 June 2016]]

Is anyone else having trouble using CKAN to install Astronomer's Visual Pack? I can't get past the startup loading screen.