I tried to turn off my main water valve and it only slowed down the water . When I tried to turn it back on I. Keep turning valve but no effect. Water won't turn back on.

Handle may be stripped, try tightening screw or remove screw and handle to determined if stripped.

Hi Pilotincmd

Grab the stem with a pair of pliers and spin the stem... may take many turns, but may work.

Otherwise, it sounds to me like you have a GATE VALVE (see image) type of shut off and most likely the valve has broken at the grooved stem and will need to be replaced. If you are on city/town water you'll need to contact them to get the water shut down so you can make the repair. If you are on a well system, shut it down and replace the valve. I'd remove the old valve and install a new BALL VALVE.

If you can't manage to get the water off tonight, or if there is an emergency charge for the city/town to come out, chat with a neighbor and see if they'll let you hook a hose up from your outside faucet to their outside faucet... cold will feed the water heater and give you hot water as well... ;)

Glad to discuss more if you want, OK?

Mark