Why would the van lose oil pressure and not start.

Is there oil in the engine?... Will the starter still turn the engine when trying to start??... More info needed!!

Many things in any vehicle can cause this! Ever since there have been safety switches, and pressure switches in line with components in the vehicles' engine to protect the engine from it's operator negligence. 1. The obvious, low oil in the engines oil pan. 2. The pressure switch is malfunctioning, causing the computer to protect the vehicle's engine from failure due to the supposed lack of lubricant. 3. The oil needs changed, i.e. when engine oil is exposed to constant heat and pressure, it becomes very thin or it loses its "viscosity" (thickness). This is a problem because it no longer has the protective quality! The switches and sensors are fooled into shutdown mode stopping the current from flowing to the components that need to be energized to complete their tasks for operation. 4. If you are experiencing this as a result of an emergency halt to the vehicles forward momentum, the problem again is that the oil in the engine may be thrown forward so fast that this also can fool the protective sensors into shutdown and the onboard computer doesn't have time to reboot before you try to start the engine. If this is the case the components, that would normally be used in the starting process, are not allowed to continue their job. This may be a project for a diagnostic tool, such as a mechanic would possess, in this case an obd11 code reader that will show letters and numbers corresponding to particular problems.