Why wont my project open on my computer anymore? Or its backups?

So after running a standalone version of my game, my project crashed and would not re open. The last time I backed it up was a week ago and even though I would lose a lot of work I decided to just delete the project and replace it with my last backup. But the backup was crashing too???

The backup file worked fine a week ago (I always test it out by adding the project to my project files on another computer with UE4, and running it to see if it works) and it did it worked fine and it always works fine, but both the original project and its backup failed to work on my primary computer. Does anyone have an idea why? Kinda scary. I don’t see how that could happen.Even after uninstalling UE4 and reinstalled the engine versions I use it still crashed. I am now only able to run the project on my secondary computer.

To backup my files I just copy the project folder and paste it into an external drive, is this not correct?

Did you make the backups while the engine was not running?

is it any C++ files in the project?