The same thing happened to me and it was caused by the Permalinks settings. If you change your Common Settings to Default, I think it will work OK. If, like me, you use Month and name, you need to append the text inside the box at the bottom of the Permalinks screen to your .htaccess file. I include the text here.
Give it a try. My blog works fine after I did that. Good luck.
<IfModule mod_rewrite.c>
RewriteEngine On
RewriteBase /
RewriteCond %{REQUEST_FILENAME} !-f
RewriteCond %{REQUEST_FILENAME} !-d
RewriteRule . /index.php [L]
</IfModule>
