I have no water from any faucet in the house. Cold water is fine, pressure as well. But when I switch any faucet to the hot water it drains the water in the pipe then nothing. The vaulve on the hot water heater is on, I have cut it off several times and back on. I have made numerous calls (friends) and I have baffled everyone. I have checked under the house and don't see any leakes and checked the main water meter and It isn't regestering any water usage so I don't think I have a leak anywhere. HELP!!

Open the drain petcock on the water heater,see if weater comes out(under pressure)
Most likely,there will be nothing.
Look where the nipples screw on to the water heater and see if there is internal rust or scale .Non factory supplied nipples cause a sort of dialectric reaction and things corrode.This must have happened over time ,and water pressure on the hot side kept getting worse.
Keep us posted

Joey might have had the right idea when he focused on the nipples on top of the tank. However, It's not rust or corrosion that concerns me. It's the nipples themselves. If you have heat trap nipples,(see image) installed I would replace them with 3/4 X 4" brass nipples. Good luck, Tom