I stored my defender 90 for three years it ran fine then now the oil pump doesnt seem to be working,would nthe oil pump need to be primed after sitting that long? I took the oil pump off and checked and cleaned it it seems to look fine,but no oil is circulating.I also ran motor flush through it,but the lifters are clattering and the oil light is on.I also removed tthe oil filter after i did the flush and it hadn no oil in it. If it needs to be primed how do you do it?

I had stored my rover for three years and it ran fine then,but recently when i started it the oil light came on and the lifters are clattering,it maybe something else clattering im not sure.I changed the oil and cranked the motor with coil wire off to circulate the oil before i started it.could my oil pump screen be clogged from the car sitting so long?