Is the cutoff a ball valve or a gate valve? A gate valve can fail in the closed (or very nearly closed) position even though the handle will turn in and out as if it was working normally. It happened to us once, but the valve was likely at least 30 years old.
How much water was coming out? If it was as much as a fully open garden hose then that valve is fine, but if it was just a very high speed, but not voluminous, flow it might still be jammed shut.
That said, if there was sand in the line when you turned the water on it might have packed up at the first 90 degree bend it encountered. If you still have the pipe open above the cutoff I would try plugging a garden hose in from a neighbor's house (or attach one through a fitting above the cutoff) and blast the pipes out in the other direction. Hopefully that will work, but it might not if there is a really huge block of sand in there. If a bunch of sand comes out you will then need to open all the valves, one at a time, hook them to that hose, and was the sand out of each. Before doing any of that you will want to extend the cut pipe out from under the house (with PEX or PVC, or even a garden hose, it is only temporary), so that all the water coming out will be outside and not under the house. (Our neighbor had a soft water canister installed a while back which lacked the filter, and all the little balls ran into his house and jammed everything. He had to back flush every line like that too.)
If you expect more sand to come into the system you need a whole house filter.