Started it last night in the snow. No power this morning. Jump start attempt getting power to it, but not turning over

It sounds like someone tried to start it and invoked the immobilizer into action. Or, the battery voltage dropped below 11 volts during starting.

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try a jump start as sounds like a flat battery

Would begin by replacing car battery and if it starts, check for codes. If no scan tool available, drive to closest auto parts store that can check this at no charge.

there should be a fusable link which if it blows will give you those symptoms. sorry i don't know where it would be on your caddy.

It seems the battery loses power over night.
There seems to be some electrical componant chewing up the battery.
Try to remove one of the battery terminal wire at night and thn fix it in the morning and thn see if it will start without jumping, if it does thn the battery is being chewed up overnight.
If after removing the battery terminal at night and refitting it in the morning and it still requires jump start ,thn the battery is faulty.
Hope this helps!

If the click is one click then that points to the starter. Make sure the battery connections are tight. If it clicks like a machine gun then it is either the battery or a bad connection. Good battery voltage is 12.6 or more and 13.6 when running. I don't know tour skill level of electricity.

check battery and connections first starting requires 300 plus amps lights about 50 so lights work but not enough to start try jump and if starts take to parts store and have then test battery

Next time it won't start turn headlights on and see if they dim when you turn key to start, if they dim its most likely starter, if they don't dim possible starter switch, Have you tried to start it in neutral position? Try that, if it starts in neutral than its park neutral switch, if not could be starter switch, Just make sure you chk. all fuses and any relays associated with ignition first.

Look in trunk, under floor cover.