My son dropped my Pentax Optio S12 now the lens won't retract and when I try to turn the camera on it just powers down and switches off

Your camera has a small chance of recovering from this very common fault: it's usually just caused by debris or dirt on the mechanism but in this case it will be either due to dislodged or broken components. You can try some of the fixes listed in this link , fix #7 is the one you're really aiming at but it's an all or nothing repair. Many retractable lens cameras have fragile zoom assemblies, but in my experience the Optio S12 has a poorer design in this respect that most and seems particularly prone to the fault.

If your camera shows absolutely no external evidence of having been dropped, then you may instead wish to see if Pentax will repair or replace it under warranty or even as a goodwill repair if just outside the warranty as it's just possible that they have identified a fault in design, materials or manufacturing of the lens unit. It would be best to say that the fault occurred out of the blue. if you choose this option, DO NOT make any attempt to fix this yourself. You also need to be aware that if Pentax judge that the fault was due to abuse (being dropped) they will offer to fix the camera at cost or will return it to you for a small fee. Given that the whole lens assembly must be replaced, and that you can buy a new replacement for around £100, you might decide that a paid repair makes no economic sense.

I sincerely hope that you get your camera working again and that you found my reply to be of use in deciding which approach to take. If so, please rate my answer.