Actually after I've tried it from a work computer it was opening login page. So enabling mod_php helped!! I've clicked on your link and it shows login page. You might want to clear your browser's cache.
After I enter info and hit login I get this error
SquirrelMail version 1.4.21
By the SquirrelMail Project Team
Error opening ../config/default_pref
Could not create initial preference file!
/var/lib/squirrelmail/data/ should be writable by user www-data
Please contact your system administrator and report this error.