I did try to upgrade my WordPress to version 2.8 from 2.7. Twice, I could not understand why when I go to my dashboard, the page is just all blank. I quickly cancelled the 2.8 installation and reverted back to version 2.7. Today, when I tried again, I was forced to search for some answers because I got hit by the white screen of death again. I actually did a backup of the database first so I was confident that nothing would go wrong this time. Turns out I was given another problem, the posts did not appear in the blog when I tried to import the backup SQL file to a different blog site.
It seems that in version 2.8, the WordPress database tables have been renamed like from posts to wp_posts. Still, the white screen of death was a bigger problem for me because I had no idea why. After some searching, the cause of this problem is because some plugins are not compatible with version 2.8. Since your dashboard is now all blank, the only way for you to reset your plugins would be to rename your plugins folder to something else and create a plugins folder. That way, you can see your dashboard again. You can slowly transfer your plugins 1 by 1 and see which one is making it incompatible.