I have a Bold deadlock on the front door of my apartment (I'm not sure exactly which model it is but it looks basically like this: http://boldlocksupply.com/premium-cylinder-deadbolt-d-8-gold/). A few days ago, all of a sudden the lever for the deadbolt stopped locking or unlocking the deadbolt- the lever turns (seemingly without any resistance) but doesn't actually move the bolt. I have tried tightening and loosening all the screws on the deadbolt but they don't seem to have an effect. The key still moves the deadbolt just fine (but if someone locked the deadbolt from the outside I would be trapped inside) as the lever on the inside is not working.
What is actually happening inside the lock to cause this? Is this something I can fix myself?