Why doesn't the main water shut-off valve to my home work?

Your gate valve is shot, not uncommon, when you replace it I would suggest a ball valve. Shut the water off at your water meter.

Since you did not specify what type supply you have:

Some houses have "captive air tanks" that provide pressure to the entire system.

Commonly, this is for a well arrangement, and not for municipal water.

To de-pressurize CAT systems; turn off the electircity to the pump> close the main supply line coming into the house > open the lowest valve in the house that's drain-able** (provide some catch system) and open other faucet/spigot valves (kitchen sink, bath tub, etc.) until the pressure is relieved.

After finishing the work, reverse the process.

**Not the hot water tank however.

The valve is bad. Replace it, then do the repair.

If you don't want to, call the water department, They will come and shut it off at the street. You can't

Old gate valves are known to fail. Sounds like it needs to be replaced. Try shutting off at the street/meter if you can.

Your turn on and off for your sprinkler system from inside the house I would think.the thing your trying to turn on is the complete curb stop for the whole house.the sprinkler water goes through the water meter first.if you want to get the mud out of the curb stop call the city that's there job to be able to shut off your house.don't worry about the water Id flush it out with a hose so the dirt bubbles out of the top.

shut off the water at your meter out at the street. if it doesn't have a lever cut off, it will have a small bar about an inch long, use a pair of vice grips to turn it or a crescent wrench. then go to the house and cut off your water heater breaker so the element in your water heater doesn't burn up. turn on the faucets outside and inside to drain the water out of the lines. MAKE SURE you cut the water heater breaker off before you drain the lines and make sure you cut the water at the meter off or you won't get the lines to clear.