I have scaulding hot water in every faucet of my house, but as of last night my shower does not! I have to turn the water control in my shower all the way to hot just to take a mildy warm shower. I checked the shut off for the hot water to that bathroom and that is not a factor. My father and father in law say it could possibly be a bad or clogged mixer valve. Any ideas and possible fixes would be greatly appreciated.

Listen to Daddy and tell me about your mixing valve. Brand name? How old? Can you shut the water off and open it up? Back to you, Tom

It's a moen shower knob one knob control. House built in 2003. Used this tub and shower just a couple times.. It's the guest bathroom turned the spicket on and get only cold water to right and left it starts to dribble but still is cold.. I don't know how to remove the plastic knob to look inside. Im not a plumber just a housewife trying to fix stuff beverly

Its a moen shower knob one knob control. House built in 2003. Used this tub and shower just a couple times.. Its the guest bathroom turned the spicket on and get only cold water to right and left it starts to dribble but still is cold.. I dont know how to remove the plastic knob to look inside. Im not a plumber just a housewife trying to fix stuff beverly

Sounds like some crud got in the hot water inlet ports in the cartridge,l(see image)where it's now clogging the flow.
To remove the handle simply pop off the center injsert and unscrew the bolt holding the handle.

Shut vthe water off off to the valve, (seei mage) and open it up. Clicking on;Installation Help / Animated Tutorial - Installing the Moen 1225 / 1200 Cartridge (http://www.moen.com/consumersupport/installation/moen0133/moen0133.cfm)
Will get you to a installation guide for replacing a Moen cartridge. Study it and open up the valve and remove thje cartridge. Check and clean the inlet ports. Now, while the valve's still open turn the water back on for a moment to flush out the supplies. You should see a full stream of hot water when you do this. Reassemble the valve and test. Good luck, Tom

Yes, your problem is that you don't use that shower too much. It is a good practice to run water in plumbing fixtures at least once a week.