When you say "no oil pressure", I assume the pressure gauge is at zero or warning light comes on. Does the engine also rattle or knock?
If the engine is quiet but the gauge or light indicate no pressure, I would guess you actually DO have oil pressure but the sending unit or gauge is faulty.
If the engine is making scary noises as well, then it is definitely without oil pressure. I hope you don't run it for more that a few seconds like that.
Most likely suspect for no oil pressure in your circumstances would be a stuck pressure relief valve in the oil pump. Replace pump.