upgraded to 2.8 and now i have no access to the site at all

First of all, don’t panic. You make a backup of your database and files, right? Then you should be fine.
Now I guess you see a white screen only? That means there are probably some PHP errors. We’ve all had that before.. What Server errorw did you get? Did you check the Server error logs (via Cpanel or SSH)? What is stated there?
It could be some new files were not transferred properly or that your database did crash – but that hardly ever happens. If the database died it can be restored with the backup .sql file. If some files were not transferred you can upload them all again via FTP and reload your site and see. Let me know..

add this line to top of your wp-config.php

define('WP_MEMORY_LIMIT', '64M');