I can't access Admin after failed 3.1 upgrade

I attempted to upgrade from 3.0.4 to 3.1 (after repeated fails of upgrade to 3.0.5). My upgrade to 3.1 failed. After the failure I discovered my entire site was down. Eventually my site returned to normal, but when I try to log into Admin I get this:

Fatal error: Call to undefined function is_network_admin() in /home/ebookchr/public_html/wp-admin/admin-header.php on line 16

What do I do now? I can’t even make a post to my own site!

I did an email backup before the upgrade, but it doesn’t appear to have been successful… I checked the email address I used for the backup and there is nothing in the inbox or spam folder.