I have Pegasus Tub & Shower Faucet, series 1000, SKU# 813-921 (bought in Home Depot about 2 years ago). Recently the hot water stops running from the shower. The hot water in sink runs good, but not in shower. Cold water is running fine. I shut the water, and removed valve. Water is dripping from where hot water should run. I would appreciate if anyone can share some ideas how to deal with this problem.

Thanks,

Are you saying you pulled and checked the cartridge? What does "remove valve" mean? Couldn't get a exact drawing of your valve but I got one close enough.
If you will remove the chrome cover plate and look on the left hand side you will see a screwdriver stop. Make sure it's open counterclockwise. Then turn off the water at the water heater and remove the stem assembly and turn the hot water valve on for a moment. There should be a strong stream from the open valve. Here's instructions on how to open up your valve. Turn off the water supply to the faucet. Start by standing in front of your faucet. Select whatever side you are wishing to remove. Look at the top of the faucet, there will be a C (45) or an H (45) on the top of the handle of the side that is being removed. Remove the cap where these indications are. Under the cap will be a screw that holds the entire handle assembly to the faucet. Remove that screw and the handle will separate from the faucet unit. The remaining parts will be 009 and the top of 006. Remove 009(valve retainer nut) with an adjustable wrench. This will then free up the valve stem cartridge. Use adjustable pliers to remove the cartridge by pulling the top straight up. This will free up the cartridge and reverse the same order to reinstall the new valve stem. Note: All rubber components must be lubricated before the new parts are installed. Plumbers Grease is recommended to complete the install of your new valve stem.
Regards, Tom