If you are not living in the desert where the cold water is hot during the summer, check to see if perhaps the Plumbing is backwards: is the hot water faucet giving cold water? I once had hot water in my toilets.
Seperate valve for outside faucet turned off, broken valve stem inside of outside faucet or handle stripped at faucet.
broken line under house,shut off valve behind toilet is turned off, blockage at the shut off valve,
what valve in what faucet exactly.
Have you turned on the shutoff valve below the sink .
The water valve under the sink is turned off or has gone bad. It is possible that there is a blockage in the faucet itself. I'd start by ensuring that the water valve is turned off, and take the faucet apart and look for anything out of the ordinary.
if it is a single lever faucet the cartridge needs to be replaced. check the supply valve under the sink first,
mixing valve in a faucet: ok I will assume you are refering to a shower valve, that is the only faucet w/a mixing valve: shut off the hot and cold water. cut out valve or unsweat it. clean and flux new valve, pipe and fittings(if used) sweat in new valve
it is a tool that resurfacese the seat on a water faucet valve
It should have both. Verify that it has two lines to the faucet. If it does, check to see if the stop valve under the sink has been turned off. It may have been leaking and turned off instead of being repaired.
Turn the water off to the faucet. Remove the handle. The top of the faucet should unscrew to get to the ball valve. Replace the valve and gaskets then reassemble the faucet.
Outside at the main shut off valve. Showers/Bathtubs do not normally have a shutoff valve like sinks and toilets. The main water valve for the house must be turned off.