I deactivated a plugin and now I can't access plugins, posts, pages, etc.

Hi. I was trying to backup my website so I could upgrade to wordpress 4.0. I downloaded a plugin – updraftplus – which was supposed to help me back it up. So, I couldn’t figure it out and ended up deactivating it. As soon as I deactivated it my plugin screen went white. Now I can’t access plugins, pages, posts, etc. I’ve gone into my cpanel and deleted all of the files within the updraftplus folder through my FTP, or what I thought was my FTP anyway. The file is still there b/c I can’t delete it, but there is nothing in it. It didn’t work. I still can’t access anything. What do I do now?