hopefully you have good backups of you database, and hopefully web directory.. what i would do is a simple restore and see if that clears it up..
you should upgrade to 1.7.5 unless there are specific reasons you are staying on an older version.
what i would do next is a fresh install of 1.7.5, then connect to your current database. if everything works, then something wierd/bad happened to your web file structure.. if that doesnt work, then you have an issue with your database, which is more of an issue if you dont have backups..
also run virus scans on your computers and check your host files, they could be infected and causing this if your webserver checks out ok.