We just moved into a house built in 1987. We have 4 1/2 bathrooms. All bathrooms have hot water in sinks and tub/showers, but one bathroom is getting no hot water in the tub/shower ONLY. When I turn the knob to hot, the water disappears and there's nothing coming out! Cold works just fine. It is one knob that you can turn to either hot or cold (left or right).

Any suggestions would be great I honestly cannot afford a plumber with the move!

Welcome to The Plumbing Pasge.
Shut the water off to the shower /tub valve and open up the faucet. Remove the cartridge and check and clean the inlet ports. While the valve's open place a pan over it and turn the hot water on to flush out the supply. You should have a full sream when you do this. If not let me know. Good luck, Tom