My pentax s51 camera lens won't open - Pentax Optio S5i Digital Camera

SOURCE: Pentax Optio M20

Maybe.
But it does seem to be a lens problem. Possibly the lens is out of sync as mentioned in another post here.If there is a grinding, the lens is probably damaged by dirt or sand.
Make sure the batteries or battery is fully charged.

SOURCE: Pentax K10D won't work with lens from Pentax K100 (film0

The lenses are probably manual focus lenses,  

1. Make sure that the apature ring is set to 'A' or automatic, 
   
2. if these are manual focus lenses then switch the focus switch on the left side of the camera body to MF 
3. If this still doesn't work, or you are having trouble with the apature ring then press the menu button to go to the  menu then press the right arrow key untill you are in the  Custom Settings, scroll through the custom settings with the up and down arrow keys until about the 2nd from bottom there is an option called "using aperture ring" set this to 2 (Permitted) This will make the camera take a image when lens is on any f-stop manually. 

SOURCE: My pentax option A10 turned black on the screen and won't open

Since the screen went black BEFORE the lens retracted, it makes me think this is a main board problem. The only other possibility is that it is the lens assembly, but since it went black BEFORE the lens retracted, I don't think that is it. I can replace the main board for $40, or you can send it to pentax in Arizona, and they will do it for about $90.
The main board is NOT something that I would suggest anyone try to replace as a DIY project. There are too many small screws, and delicate connections to deal with.
You can contact me at: mrfixitmark at comast dot net

If you just want to sell the camera as-is, I also buy all pentax a10, a20, a30, a40 cameras, in any condition.

SOURCE: pentax camera espio 738g zoom

The camera has a faulty capacitor inside the circuit board. Having it repaired generally cost more than purchasing a replacement camera. Capacitors store the power needed to operate motor drives when needed. If they get a hairline crack on the outer shell they will lose there ability to operate correctly such as yours is doing

SOURCE: I have a trouble with my digital camera. When I

Hi Noodle
One of Pentax's strengths is that that you can use lenses from the late 1960s on them (via an adaptor). However, I'm assuming that you have a bayonet fitting lens - but as you say 'my manual pentax' could it be that they are not autofocus lenses?
If autofocus is switched on and you have a manual focus lens, you have to have something in focus in order for the shutter to fire. (with no lens fitted it doesn't seem to matter). Switch the camera to manual focus (where you can shoot out-of-focus stuff) and see if the problem is still there.
If it is then it spounds as though there is something amiss with the camera to lens coupling.