When the oil pressure gauge reads "0" and there is obviously oil pressure, as you describe, there could be a problem with the sending unit, the gauge, or the wire connecting the two. Let's try to figure out which.
First, find the pressure sending unit. I don't know where it is, but it will have a wire to it and it won't be the temp sending unit near the thermostat/radiator hose although it may look similar. Check that the wire is connected. If it is loose or disconnected, you'll read "0." This is the cheapest problem to fix, and it does happen!
Wiggle, or try to wiggle, the connector at the sending unit. Remove it, check for corrosion and put it back on. Do this a few times to wipe it clean. Did that bring the gauge back to life? Great!
Oh, it didn't?
Next, try 'grounding' the wire - remove the connector from the sensor. A helper can be useful, at least to watch the gauge. Touch the bare metal of the connector to bare metal of the engine or chassis, or use a short length of wire if the connector is recessed. This will put a 'short' or zero-resistance signal to the gauge and give you a maximum reading.
If this 'grounding' doesn't get the gauge to move, the instrument cluster connector or the gauge itself could be the culprit. That's an advance DIY project that others will have to help you with, or leave it to a Tech.
Good luck and good hunting.