I know there are tons of posts on this issue in the forums. I've read those posts and tried some of the advice there, even though many of the posts date to 2005 and apply to WP 1.5.
Deleting cookies and clearing the temp cache did not work for me. Let me describe the problem: when you click the "login" link on the sidebar, you are taken to a blank page. After clearing the cookies, you are taken to the regular login page and then, after entering the correct username/password, you are taken to a blank page.
However, by clicking an "edit this" link on a permalinked blog post, I can access my admin panel. But come to think of it, this may no longer work, either, since I've just cleared my cookies and cache.
I emailed my site host, first, and to make matters more confusing, a techie wrote me back to say he could access the admin panel just fine on his end. I've tried it now on three different computers, all of which I have used in the past to post, and all have the same problem for me. Any ideas?
Incidentally, I am running WP 2.0.3. My host has not provided the 2.0.4 upgrade, so I am unsure whether I can download 2.0.4 and then upload just the wp-admin.php and wp-login.php files. I know that was a suggestion in some of the other forum posts I read.