Of course it may have something to do. Any other suggestions ?
I *think* you were trying to say that the theme has something to do with your login (perhaps you were trying to type in: "Of course it may have something to do with it" in response to my "the theme has nothing to do with your login")?
If that so, no - the theme *doesn't* have anything to do with your login. If your login will not function, and you get a blank white page when you try to visit your administration panel, there would have to be some coding in the theme that overwrites (or adds to) functions in your admin panel - or the theme would have some sort of database stuff going on that would mess up your connection - but that's kind of odd for a theme to add in. The theme has to do with the look of your site - but nothing whatsoever to so with how your administration area looks or functions.
Now, if you're used to using the "meta" are to get to your login, then yeah, I could see how you would think that, because the only way you know how to get to your admin area is gone. But the URL to your admin area will be:
You can get to your admin area at any time without ever having to visit your site first.
And again (and as Michael has reiterated) FTP into your server and delete the theme if that's what you suspect did it. It's possible, I suppose, but as a general rule, themes have nothing to do with your admin area.