A couple of days ago I started having problems loading data into my ArcMap program. I now get the error message: "Failed to connect to database, An underlying database error occurred, class not registered." I believe that this started happening when I allowed Microsoft to make an update to my windows software.
Any help would be greatly appreciated.
This is a connection issue between ArcMap and your database. Make sure your database name / userid / password / etc. in your connection are correct. Talk to your DBA (if this is not a file geodatabase), especially if "nothing has changed".
Other solutions can be found by searching on your error which may fix that problem, for example see