First thing to check...Go to Courses on the left side of your screen and select All Courses at the bottom of the list in the panel that appears. Scroll down and see if you can find the course in the list. If you do, then it means that the course had an end date for the term and that date was passed. All of your stuff is there, you just need to export everything from the Settings menu of the course to back it up. You could also feasibly copy elements from the course into another course, but if you have a lot of stuff, this could take longer than an Export.
If you do not see the course on the list, that could be an issue that may require tech support. You can click on "Help" in the menu on the left side of Canvas and select to submit a ticket. You might also talk to anyone on your end that might have admin level access to your district/university to see if they can assist.
