Sims 4 crashing on startup, Blue Screen of Death Sometimes

Take the whole sims 4 folder from the My Documents/Electronic arts folder and place it on your desktop somewhere. Then run the game (it will generate a whole new Sims 4 folder) When you do this if the game starts then you need to save the game and exit.

Slowly start adding your saved games from the old sims 4 folder (now on your desktop) into the newly created set back in your my documents/Electronic arts/sims 4 

Then add back your mods a few at a time (I make a folder inside my mods folder called testing) and then run the game after each batch you add to see if the game starts. If the game starts take out the files from the testing folder and add them to your mods folder and add more to the testing folder and start the game again. As soon as the game stops loading you will have found a file that is causing the problem in the last batch you added and then its just a process of elimination (one by one taking them out until the game loads). Its not easy but its the only way. There is a sims 4 mod conflict detector at Mod the sims 4 you could try that out too its made by scumbumbo.