Most of you will be aware of the below, but I think it's beneficial to have this summarised. Therefore:
There are 3 basic game breaking problems one may come across when playing Skyrim. It's important that you can differentiate between them and know what may be causing them, and how to fix them.
KNOW YOUR PROBLEM
The difference between CTD, ILS and freeze
Please note that Skyrim engine is a strange animal and the below definitions will not always be accurate. I base the below on my own observations and experience, and if anyone can add something or correct me, feel free to post and I will edit this thread accordingly.
1. CTD - Crash To Desktop
What is it? CTD occurs when Skyrim application is suddenly closed and you get kicked out to desktop.
What causes it? The most likely culprits are either (in)famous 3.1GB RAM limit crash OR mod or script conflicts. The first one occurs mainly when you have too many high resolution textures loaded up and since Skyrim is unable to utilise more than 3.1 GB RAM when it reaches that limit, your game crashes.
How to fix it? If it's texture size related - either use ENBoost program to allow Skyrim reduce memory use or if you don't want to use it, reduce size of the textures you use. Mod conflicts often can be fixed by identifying CTD spot, making a vanilla save there and gradually increase a number of installed mods (say, 5 at a time), to see when the CTD will occur, so that you can identify the mod that causes your CTD.
2. ILS - Infinite Loading Screen
What is it? Infinite Loading Screen means that you are stuck on a loading screen forever. It occurs during transitions from one area to another or when loading a saved game. The animation keeps playing, the quotes change, but the game never loads up. For area transitions it happens most often when exiting an interior or exiting from a city into Skyrim land. Some ILS-potent spots were identified as follows:
- Dragonsreach -> Whiterun loading screen
- Jorvaskaar -> Whiterun loading screen
- Markarth -> Skyrm loading screen.
What causes it? ILS means that the game engine is not capable to load all the information it requires and quite often there is no definite solution. It's basically "You have too many mods installed" case. The game is trying to load all the meshes, scripts, textures etc., and it's just too much to cope with.
How to fix it? The solution is to decrease the number of mods. It's recommended to remove LOD mods in the first instance.
3. Game Freeze
What is it? We can talk about game freeze, when your screen (yes, you guessed right) freezes during gameplay. Neither keyboard nor mouse work, but the game doesn't crash to desktop.
What causes it? Game freezes are often caused by Papyrus scripts clogging. The game engine can only cope with so many scripts running at the same time and if you will have too many mods that add scripts, you may come across freezes.
How to fix it? The freezes can be difficult to diagnose. Use your intuition.
An example: If your game often freezes during combat, check which combat mods are script-heavy. Enhanced Blood Textures, Burn Freeze Shock and Deadly Spell Impacts are good examples of mods that can cause your game to freeze (I am using this example, as it's confirmed information).
Remember - there's no 100% confidence that it's any one mod. It's the overall script load and often removing ANY of the mods can solve the problem. You only have to decide which of the mods you need least.
Another method is to enable Papyrus logging, play the game and once it freezes, check last entries in the Papyrus log - sometimes it will contain some indication at which of the scripts failed. The solution is to reduce the number of scripted mods.