Oil in car not getting to engine - bad oil pump or clogged oil screen?

I´ve the same problem, but my engine doesn´t start i was driving full throttle and then is just switched off, then i couldn´t start, i put 2 oil litres but it still don´t start, when tryin´to start engine, low oil light gets on, do you have any idea if it is my oil pump? y don´t know where it locates, my vehicle: 95' Mercury Villager GS for contact rpgdomain@hotmail.com Greetings