New to modding and now in trouble so please be patient. Here's all the info I think can help you diagnose this:

My game CTDs on the load screen but appears to be ok starting from a previous character's save or if I start a new character.

I checked the plugin dependencies manually in the NMM and nothing is obviously out of order.

I did notice NMM lists Skyrim.esm and Update.esm in gray at the top of the list of plugins. Both are present in the Skyrim/Data directory.

There are some mods in NMM that are red because they depend on missing files. None of these red mods are active.

Running SKSE 1.7.3, TESV.exe 1.9.32.0, both with Administrator privileges. Both are in the Steam/steamapps/common/Skyrim/ folder

Just before this happened I was looking through LOOT's interface but I don't believe I asked it to do anything, maybe I did, can't remember.

Ok all - do your magic; what do you suggest?

Many thanks!

Update: Unloaded all my plugins (around 52) and started building it up again. The Campfire mod and Enhanced Town and Cities mod are definitely prime suspects. I'd like to get Frostfall back in the list but I believe it has a dependency on the campfire mod.

If te game instantly crashes on load, it's a missing master (you have a mod activated without all of its masters activated). If the game loads to the main menu but crashes when loading a save but will start a new game, then it probably means that save is fubared.

Thanks, Turija - I didn't know that a missing master file causes the game to crash on load. That must be what happened but I have no idea why.

The good news is that everything is almost back to normal.

I deactivated all the mods (which cost me a few Campfire and Frostfall perks and assets - so another lesson there about what happens when you deactivate a mod in mid-playthrough), then learned how to scrub the master files by using TES5edit. I then started ordering them properly with LOOT. Props to GamerPoets and Gopher for their instructional videos which made all the difference.

I gradually rebuilt the game and am almost back to where I want to be. The only major change remaining is the addition of Enhanced Towns and Cities - which has a long, long readme with lots of requirements that need to be addressed manually (... if you select this plugin, copy file x to directory y) etc.

I now track my load order in a text file on my phone as there doesn't appear to be a facility for archiving this info in NMM. I'm a little surprised there isn't an app for this. Every time I activate another mod, LOOT makes some small change to the load order.

I'd like to learn more about TES5edit is doing and displaying so any resources you can recommend would be great.