Well projects tend to get harder to open the longer you work on them, your project must have gotten too heavy for your computer to handle. Have you added anything that could damage performance lately? if so, you can either trim down some of the objects in your scene or you could find another way to make them more efficient.
Reinstalling Unity didn’t end up working. And since my other computer with as much memory was playing the projects, it didn’t seem like it could be the project getting too heavy for the laptop. What ended up working was resetting the PRAM, surprisingly.