How can I deactivate a device administrator when uninstall is grayed out?

I downloaded Aptoide (to download apps) i got a critical app from aptoide and it turned into the device administrator.
whenever I tried deleting it, it turns the screen black, I had to take the sim card out, then back in.
I got another device activator-safe one, then I could deactivate the other. Dont know if it works, but worths a try

Yes. Tell us how you get on. Also, booting into Safe Mode before deactivating might help.