I think the oven is from 1974. The lock (for self-cleaning oven) was accidentally put on by pushing the lever to the right. When I returned the lever to the left, the door would not open. The self-clean had not been activated. An appliance repair man recommended that I run the self-clean, which I did, but it will still not open. I also unplugged the range and plugged it in again, with no results.