1997 Cadillac Catera oil in water

You need to get it block and pressure tested could be a blown headgasket cracked head or block, intake manifold leak-

By not starting, give some more info. Does it crank and not start, or no crank and no start. The oil in the water is more than likely a leaking heat exchanger(oil cooler) in the valley of the engine.

Yes it would start if it was the oil cooler, and probably if it was a head gasket, unless that was severely letting water in the cylinders. If it was a head gasket, you would more likely have water in the oil, unless the leak was where pressurized oil was passing to the upper end. That is a pretty small area. On the other hand, a greater chance of pressurized cooling water passing into oil drain passages from the head is more probable. The reason I speculate oil cooler, is because the oil is pressurized, and most of the time higher than cooling system pressure(at least at higher rpm's). The cooling system would also remain pressurized until the engine cools. Try pulling back one of the air snorkel tubes and spraying some carb cleaner or starter fluid in the throttle opening, and see if it starts. That would indicate a lack of fuel. If you can have it scanned for codes, it could have a failed crank sensor, as well. 97 Catera did have an issue with head gasket leaks, but it was generally external, due to stampings in the block deck at the sealing surface.