sounds like oil pressure sensor is bad to check the oil pressure remove sensor and screw in oil pressure gauge if the engine isnt making a noise with oil pressure reading 0 then it is your sensor that is bad
Is the engine making any ticking or tapping noises? If not, then it is your sensor or guage. Screw in a manual guage in place of the oil pressure switch and get a reading. If there si no noise, chances are it'll read normal. To test the guage you need a variable resistor box (guage tester). Easier to just replace the sending unit and see what happens first.