cstone Have changed the PHP version on IIS
Not that I think that this is relevant to your issue but what version did you change to?
If it is 7.2 - 7.4 then when you restore you would not be able to run the old version of osTicket.
Well unless you have multiple versions installed and point the IIS site to use the old version of PHP.
Either way I would recommend that you restore the DB, point the IIS site to the old PHP (if you can) to get the site back up and running now. When I upgrade my production sites (also under IIS) I always do it on a clone of my production site first to make sure that everything is going to work. To do that properly with out affecting the production site you create a clone of the database (although a slightly different name, and create a new test site in IIS with a copy of the core files. Then edit the ost-config.php to point to the new clone DB).
cstone UPDATE ost_thread_event A1 LEFT JOIN ost__ticket_thread_evt A2 ON (A1.thread_id = A2.object_id) SET A1.thread_id = A2.id] Unknown column 'ticket_id' in 'NEW'
So the error says that ticket_id is an unknown column ... have you looked at your database table ost_thread_event to see if it exists?