"How to fix a broken water valve handle", is a video on How to Fix Shower Valve Stems that are Stripped.
When your shower knob turns, but no water comes on, the valve could be faulty and in need of servicing, or it could just be the handle.There is an easy way to tell.If you want to check out the notch on the valve stem, you have to remove the handle.There should be ridges on both.
If the handle or valve stem is stripped, the best solution is to replace it.If you don't have a specialty faucet, you can usually find replacement parts at most hardware stores.Don't worry.It isn't difficult to replace it, and it is usually not an expensive part.There are a couple of tricks you can use to get the valve to work.You might be able to not replace any parts at all.
You may be able to fix the problem with a screwdriver or wrench.Remove the cap that protects the set screw on the handle with a flathead screwdriver.A circle with blue on one side and red on the other is the logo of the faucet manufacturer.You might have to look for it on lever-style handles.
The set screw needs to be tightened.To tighten screws that hold the handle from the top, you need a screwdriver and a wrench.If the screw backed out, your problem is solved.Put a thread-locking compound on it to stop it from happening again.
Wrap the valve stem with plumbing tape if you can't tighten the screw.You want the handle to be tight, but not so tight that you can't get it back on.The handle may work if you replace it and tighten the set screw.This isn't a permanent fix, but it should last until you have time to replace the valve stem or handle.
You'll have to replace the entire valve if the stem is stripped.To remove the valve, you have to turn off the water to the shower.You might have to use pliers to get the valve out if the shower handle is stripped.If the valve is stuck with scale, and it's old enough to be stripped, you may need to buy, borrow or rent a valve removal device, which is a corkscrew-like device.
Once the valve is out, take it to the hardware store, consult the manufacturer's website, or check an online plumbing parts supplier for a replacement.