If you really don't have any oil pressure then either the low pressure oil pump is bad, you don't have any oil in the pan, or perhaps the sender is bad. The low pressure oil pump feeds the high pressure oil pump so without oil pressure nothing is going to happen.
If it doesn't turn over is your battery dead? Or do you mean it won't start? If it won't start check the oil level in the HPOP reservoir . It should be about an inch from the top. And yes check the engine oil. The injectors use high pressure oil to run and if there's no oil then they won't run.