I have upgraded my wordpress version to 2.8 and now I am able to do login into the wordpress admin area and receives blank page after login. I have searched the solution and described it here:
1) Either rename the Plugins directory from FTP or deactivate all Plugins from database.
Refer this: http://www.bestwpthemez.com/wordpress/how-to-disable-all-wordpress-plugins-from-the-database-2205/
2) If option 1 fails then rename theme folder in wp-content/themes via FTP to cause WordPress Default theme to be place into service.