You "assume" 2.7? First, let's get the version number. You can log in to your wp-admin right? On the "dashboard" somewhere it will say something like "You are using WordPress xxx." - in 2.7 it's at the bottom of the "Right Now" box. Check that and share the version.
Second, you say "I am using the online version of wordpress" - do you mean you are using a free blog on WordPress.com? If so, you are in the wrong place. These forums are for people hosting the WordPress software on their own hosting account or server. For support of WordPress.com sites, please go to WordPress.com and click on the support tab.
If you installed the software on your own hosting account, try removing the files in the "wp-admin" folder and uploading them again - could be a corrupt file.