It sounds like your theme may have a z-index value for the menu that is greater than the popup. Not unusual but it would need to be analized to see what the exact problem is.
Do you know how to check the CSS for the different areas to diagnose?

would that just be in the style.css? One thing that is weird though, if I click on the my profile, then click on new posts, it shows up fine

Brandon was probably meaning the CSS for the Simple:Press theme you are using. If you locate the CSS for the .ui-dialog class you could try putting a z-index on that.

is there any documentation in the codex I can follow along for that yellow?

okay this strange, it only happens on the main forum page, if I am on a subforum, profile ect, it works fine

What, perhaps, you should be doing is checking to see what styling is being applied as then we will know where to correct things if needed. So – do you know, by any chance, how to use the web console that comes with your browser? And if so do you know how to inspect elements and look at the CSS being applied to them? (Where you can also change the CSS to see the effect)

yes, I know how to inspect elements, just trying to find the right one

The outer container of the popups is a class of ui-dialog

after testing further, I found some other issues, so I reverted back to my old theme, and now there is no pop up at all on the main forum page, can I have one of you take a look and see what you think? Thank-you.

would need a url to take a look…

Mr Papa said
would need a url to take a look…

here you go

http://thehomesteadingboards.com/forums/

The .ui-dialog class in your SP theme css file (default.php) requires a z-index of at least 1.

This is actually the opposite of all other sites we have encountered since WordPress 3.9 where we have had to recommend people remove the z-index completely. I have to admit I am stumped as to why your WP/WP theme/SP should be different. But hey – that is one of the things we all love about WordPress… every site is unique!

So – it depends which theme you prefer to customise. You could probably put this in your WordPres theme:

.ui-dialog { z-index: 1; }

or just add the z-index to the SP theme where you will find an entry already in place for this class.

The good news is that 5.5 of SP will introduce child themes making customisation a lot safer from updates.

thanks yellow, I added that to the theme custom css and it works fine

yellow, what would I add for the pop log in screen on mobile? I just noticed having a issue on that as well