My 2005 Yukon Denali won't start. When I try to start it, all the lights inside flicker and nothing works at all with the key in. The engine doesn't make any noise at all when I'm trying to start it. What's going on?

Remote starters normally only let you do that. You will need a key made in case the remote starter fails, and they do often. The dealership can do it from the VIN Number. You should really have one for use and a spare.

under the hood I would check the thermostat to make sure it open so that the hot antifreeze reaches the sensor to make the fan start

most likely a engine or body ground could have been damaged or left of altogether by trans guy.

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did you tune it up after 100,000 miles check fuel filter and also inspect all vacum hoses

This can be fuel pump related or just fuel filter related, spark plugs and injectors.
When engine is cold vaporization of gasoline is minimum. When fuel vapor is less than required and the fuel mixture is not ideal, ignition happens harder than it does under ideal running conditions of engine. When fuel pups is sweak, or filter is limiting, or fuel injectors are not injecting gasoline with improper pattern inside engine, or just becasue of corroded spark plugs, cold engine faces difficulties during first ignition.

PS: sometimes car starts and stalls.it fails to start once more. this can be a sign of broken crank position sensor. FYI.

Define - It attempts to turn over but won't catch and run ???? When you turn the key to start does the starter engage an spin the engine ? This would be a crank no start condition . If the starter doesn't engage an spin the engine this would be a no crank no start condition . Sorry to ask but i have only been an auto tech for thirty years an have heard a lot of different discriptions for these simple actions . crank no start or no crank no start . Very different diagnostic procedures . So when you turn the key to start , does the starter engage an spin the engine ,but won't start an run ?

Hi there !

I won't say its an alternator problem because the alternator only charges the battery when its on, And it should start with the jump cables even if the battery and the alternator are bad. your Issue is not clear. Does the car start when you jump it ?

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Check all the grounds and cables at the battery and on the body near the battery