I can't empty spam trash or mark comments to delete them

Try deactivating all plugins. If that resolves the issue, reactivate each one individually until you find the cause.

If that does not resolve the issue, try switching to the Twenty Fifteen theme to rule-out a theme-specific issue (theme functions can interfere like plugins).

The same thing. Is not working at all (it keeps redirecting me to homepage) and I don’t think this is from themes or plugins, this is a core problem maybe. Not sure…

Ok, if the problem continued with all plugins deactivated and the Twenty Fifteen theme active, then we can definitely say it’s not a plugin or theme issue.

Try downloading WordPress again and delete then replace your copies of everything except the wp-config.php file and the /wp-content/ directory with fresh copies from the download. This will effectively replace all of your core files without damaging your content and settings. Some uploaders tend to be unreliable when overwriting files, so don’t forget to delete the original files before replacing them.

This is impossible… I did everything you said, first deleting the core files and re-uploading again and the same. Must be something from database.

Ok, I think maybe I misread your first post, taking a closer look.

I really don’t know why I can’t delete all spam comments by marking comments or pressing the Empty Trash button.

That’s normal, Empty Trash only empties the Trash, it doesn’t empty the Spam queue.

I can only delete spam comments one by one, and the problem is only for Spam folder, the others are ok.

Do you see a button labeled “Empty Spam” when browsing the spam queue? Try pushing that button.

If you don’t see a button labeled that, are you currently (or were you ever) using the Akismet plugin?

The button “Empty Spam” is there. When I click it it goes to home page (as mentioned in the main problem).

I used Akismet plugin but I removed it, as I don’t need it anymore. I’m also using W3 Total Cache with iThemes Security.

I remember that long time ago it, the button was working ok, but suddenly don’t know why is happening that.

Hm, something must be interfering with the buttons operation, or maybe the database tables need to be repaired.

Access your WordPress database via phpMyAdmin (most hosting providers offer this in their control panel), check all of the tables, and choose “Repair tables” from the pull-down menu.

I just did a repair and optimize to all tables. Still nothing ??

Forgot to mention that I use W3 Total Cache and iTheme Security, not disabled. but since I already tested with everything off… also used Akismet in the past, but I got rid of it.

Ok, so when I mentioned “try deactivating all plugins,” I really meant all of them. Please try that.

I know those two are important to you, but they’re also the most likely causes of your problem. If they wind up being the problem, there are plenty of alternatives.