1997 Cadillac STS '97 Cadillac seville sts only turns over

He is right about reading the codes, it will point you in the right direction, but some simple tests can be done to figure out what system is broken, fuel, spark, compression, you need all three, here's a few basic tests, I do recommend the scan too! Start with the basics, and work your way up, Last tune up was? Wires plugs ALL filters? If all that is ok, check for a stuck EGR, then test fuel pump pressure, If it won't restart, determine what's missing, the engine needs three things to run, Spark at all plugs, gas to all cylinders, and compression in all cylinders, tho an engine may run lacking one in one cylinder, it won't run very well!
https://www.2carpros.com/car_repair_video/test_fuel_injection_pressure.htm
Go here and checkout our video.
https://www.2carpros.com/car_repair_video/test_engine_ignition_system.htm
and this one!
If the check engine light is on, read the codes, the computer is trying to point you in the right direction.
https://www.2carpros.com/dia/how_to_scan_trouble_codes.htm
Compression test:
https://www.2carpros.com/dia/how_to_check_compression.htm
Readers can be purchased by following the link in my signature file, this is a must do step for all computer controlled cars.