Minecraft world not callable

My problem is that I pulled a world of mine from the saves folder of .minecraft on a USB stick without first copying it. Now this world was completely out of the folder saves outside and on the USB stick. However, if I put this world back into the saves folder and then start Minecraft this world is not found, even though it is in the saves folder.

Can someone help me solve this problem if it is possible?

It could be that during the transfer the level.dat file broke