cannot access admin panel after upgrade

hi,

i decided to finally upgrade my wordpres from 2.7 to the latest 2.9, after taking a while to ‘upgrade’ i can no longer access my admin panel.
after i log in all i see is a blank screen. so i can’t write new posts, see my stats, check my plugins, anything! I have no idea if it was even upgraded properly, clearly something has gone terribly wrong.

i can still ‘see’ blog and all the posts and comments are still there. its just the admin panel i cant access.

i backed up the db before the upgrade, using a plugin but i have no idea how to get everything back to normal.

any help would be appreciated, we have been without a blog for several days now and there are people relying on me to get the blog back up.

thanks