I use the portal and go to the Atum dimension but when I get there it’s nothing but sand. No mobs, no pyramids, nothing... playing on 1.7.10

We're no longer providing support for 1.7.10.

Likely this is one of two things:

1. You didn't download directly from CurseForge

or

2. you have other mods causing conflicts

We also do not provide support for either of these things.