My whole level turned black and the fixes don't work

Hey Guys!
I have an issue and as far as I’ve read, many have had something similar before me.
When I rebuilt my lighting after a long time, the whole level (landscape, meshes, player, everything) turned completely black (except for the sky).
I’ve read through the error message I got and I also searched on the internet what other people did to fix it, and apparently, it’s a lightmap issue and also has to do with the number of meshes.
So I’ve started with reducing the lightmap value for all the meshes, rebuilt the lighting, didn’t help. I also increased it because some guy actually said I have to increase it, also didn’t help. I deleted the lighting objects, I moved the landscape with meshes, I did pretty much eveything that I thought might have to do with and it still didn’t fix it… Can somebody help?
Thanks in advance!