Actually, I had disabled some services in msconfig recently. I just re-enabled everything in msconfig and device manager and rebooted, now the turn off adapter option is there.
When I click it in the right-click menu, nothing happens.
When I check it in the settings dialog, the following error is displayed:
This is the same error that was happening before. It just says that the discoverability settings were not saved, but the power off setting is also not saved - when I re-open the settings dialog the Turn off adapter box is unchecked again.