[iamrfixit]

If the outdoor spigot was still turned on and has froze, you're likely going to need that valve. The expanding ice will split the pipe or can even split the spigot valve itself apart. It probably won't even leak until it thaws a little and begins to drip, the water can suddenly start to flow, either inside or out. You almost never get by with freezing at that level of cold without getting some kind of damage.

You need t try about whatever you can to get the valve to shut off. Once it's turned off, remove that little cap on the left side to drain the water from the line, unless you can thaw out the spigot enough to get it open to drain.

If you can't get the valve closed, you may need to know how to shut off water to the whole house.