Question about oil pressure...

EDIT: I just realized that there is r/cartalk, I will cross post this there. Sorry about that

I have a 1998 Chevrolet s-10, and until an hour ago, has worked great. I tried to start it and you can hear the engine crank but it will not start. There are no warning lights on the gauge cluster, but what I have noticed is the Oil Pressure gauge is at 0. On a scale of 0-90, from what I assume means PSI it is at zero when the car is on, but the engine is not running. I added some oil (10w30) because I did notice I was low, but not dangerously low, and there is no leak. What could be the cause of this?