All of a sudden I don’t have permission to do anything?

All of a sudden last week I wasn’t able to post new content (it would go to a screen that asked, “Do you really want to edit this post?”), add new catagories (I didn’t have permission for that) or change themes (half of the themes I uploaded didn’t show in the theme gallery). I believe I was using 2.0.2 or 2.0.5. I figured since I wanted to use newer themes I might as well upgrade to 2.1.2 (which was the version I had found at the time). I did, but the same problems persisted. I deleted all my wp files and reinstalled again. Still not working. Just now I used an automatic installer (through fantastico on my c-panel at electrickitten.com) to install the newest version of wordpress on to my site, but it’s still doing the same thing.

Anyone have any idea what might be going wrong?