If you use UC (aka Ultimate Collection), every time you repair your game, it partly returns to its default state. Which means... if you use a default replacement for the startup screen and/or any lightning mods, they will be reset. Which means... you have to reinstall them.
SOLUTION: Just keep a backup folder of your Origin Games folder in Local Disk C. And don't repair your game. Trust me, the problem isn't in the game files. It is in your game. Most likely an incompatible piece of CC, such as conflicting mods or missing Master Mesh or something similar.
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Classic Sims [THE SIMS 2]
Non-FictionIn which I teach you awesome things about The Sims 2 that I've learned over the past couple of years! Obligatory for Beginners! But Intermediates can learn a thing or two from here as well.