It most likely has lost prime, especially if it had oil pressure before it was stored. Some engines have the oil pump above the oil level in the pan. This happens when all the oil drains back down and the pump is dry.
A couple of solutions are to start it and rev the engine and hope to get pressure. A risky move since everything is dry.
The other is to remove the oil pressure gauge tube and pressure feed oil back through the system. This can be done with any means of pumping clean oil under "some" pressure. A new, clean pump up sprayer will work, or anything you can rig up to pump clean, light oil.
Just adapt a fitting into the block, pressure it up for an hour or so, then replace the gauge fitting and see if it gets oil pressure.