I had a working install on WP 2.5.1 with 3 themes other than default and Kubrick. I installed another to get a better look at how it might function, "ultimatebaseball," and immediately the dashboard turned into a totally white page with no showing errors. I had another web browser open with the site in it and when I refreshed, it also went white and no errors.
I have no idea what I did since I didn't do anything different than my other installed themes. I have no idea of where to look in the file structure because I would know what error to look for.
After searching here and on Google, my last thought is to delete everything and reinstall from scratch. I do have access to all the files, content and DB but, I'd rather learn how to fix the error than just delete things. I can't learn anything by doing that.