Bad Hadraulic Lifters, Maybe?

You gotta prime a new oil pump with oil before installing it; if you did not it never suck any oil up and just froze from lack of oil.

Pour some oil in from the top of the oil pump and then I like to drop the pump in a small tub of oil and spin away to get it working. Messy but works. You never ever install a dry oil pump--unless you can pressure feed the oil lines from the filter area--shop equipment stuff most of us do not have