You could rename your PST file then when you start Outlook, keep clicking on OK and Open until Outlook opens in full.
It will create a new outlook.pst file in your user profile folder after objecting that there are missing folders and so on.
Obviously this will mean all of your contacts, appointments and so on will need to be imported from the renamed PST backup file, since your new outlook.pst file will just be a series of empty folders.
Try creating a new appointment in the new pst file and if it works, run the import to pull in all your old pst file contacts, appointments, calendar, emails and whatnot.
If it doesn't work, rename the new past file, and then rename your backup to outlook.pst again and we'll try something else.