Admin Functions Broken

Ok, I don’t really know how to explain this, and I have no idea what I did to break everything. Here are some of the symptoms:
-Can’t login. When I go to the login screen and enter my information and click the button to login, it just goes to a blank page. Nothing on the page, nothing in the source. And it doesn’t log me in.
-From a session that’s already logged in, when I do something like try to add a link or edit a link category, when I click the button to perform whatever action it is, it either goes to a blank page or a page that just has the footer information for the admin section (the link to wordpress and the support forums).

All that I remember doing this morning was that I had to clear out the database table that holds the information for what plugins I have, because it was showing some in there that I’m not still using. Also, I installed the PHPExec plugin and the Plugins Used Plugins.

Anyone have any ideas what I may have done and how to fix it?