99 Mercury Cougar oil light came on

We stopped immediately and put oil in. Less than five miles down the road the car lost power and turned off and would not restart. After letting it sit for a week or so it still wouldnt start. Nothing we have tried has worked. My boyfriend is a certified mechanic but he is stumped that's why we took it to the dealership, but unfortunately all they did was take my money and give me wrong diagnosis and kept telling me to bring it back to be retested and I paid $65 each time for then to mmu help. I did that five times before getting frustrated.