What took your blog down, and what brought it back up? Whatever happened, that's your cause and solution. Assuming it was something at your server then simply replacing all the files in your admin and b2evocore folders should fix your issue. From your backups assuming you have backups, but if not simply download another copy of your version then upload the files in those two key folders.

It went down and came back up by itself, I didn't have a chance to research what the problem was because by the time I sat down to look into it, it was back up (of course, I didn't try to edit the blog then).

I'm at a complete loss....