It is possible that this branch of the water system is clogged with small rocks. You could install a tee with another shut off valve and hook an air compressor or portable air tank to the line to dislodge the clog. You can charge it with air and then turn the air off and turn the valve on the side outlet of the tee to see if flow has been restored. The rocks might be big enough that the angle stop might need to be removed. If it does, you could install a full port ball valve and an adapter that would accept the compression end of the supply line. If this is the case I would most certainly install a whole house water filter. This is always your first defense for such a problem.