[Theme: Base] Cannot activate any other themes.

I opened my admin panel to find “The active theme is broken. Reverting to the default theme.” I also had a 2nd message, “ERROR: The theme directory “base” does not exist.”

I deleted the “Base” theme because I wasn’t able to make any changes in the theme section of the admin panel. I can only remove themes. I have been able to add themes via FTP, but I am very limited in what I can do in the admin panel. ALSO, none of the theme thumbnails are showing.

Is there anyway I can change the active theme? It is stuck on “Base” but Base does not exist because I deleted in hope of fixing the problem. I also cannot find the theme to re-upload it to see if that fixes it.