Cannot edit, write or delete

After over a year of functioning perfectly, my WP install suddenly will not let me edit, write or delete posts, pages or comments.

Any time I hit a Save button, I get a very long delay, followed by the dreaded Page Cannot Be Displayed error.

I tried updating to 2.2, but the problem did not go away.

I’m also having a weird login issue—if I log out, it takes a dozen or so tries before I can finally log in again.