Turn key lost all power

Resetting the Passlock system should fix it. If it doesn't you need an auto electrician or an auto locksmith.

https://www.google.com/search?q=2001+gmc+yukon+security+system+reset

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Yes, it has to do with the ignition switch. but just as possible could be a battery connection from the battery to the switch. So, sometimes turning key to ON causes no dash lights or warning lights to come on?
That sounds like a bad switch, or more likely, a bad battery connection or a bad connection between the battery and the switch. First thing to do is check the charge of the battery, it must register at least 12 volts. 12.6 volts is the ideal for a good and fully charged battery. Clean and tighten all battery connections.

Sometimes when you have a poor connection, from looseness to corrosion, and you turn key and see all warning lights and gauges come on, and then turn key to start and everything goes black...that can happen because the power surge causes the bad connection to come apart. So check for loose or corroded connections.

the manual covers this, the IMMO is active. ?
car will not crank, is that it? it must crank to start. so cranking is 1st.
you turn the key and the IMMO LAMP must NOT be showing its blocking starts. is it
do you have full batteryvoltage. 12.6v at the battery terminals
I waited a few minutes and the dash board lights started coming
that means the battery is dead.
the dash waring lights must come on ,at key on, fast
if not we fix that first. that means power lost, 12vdc power loss.
use a voltmeter. at battery

starting withthe battery,check and clean ALL connections as something is not making proper contact.make sure the cables are good, clamps tight..work your way to the starter solenoid and check contacts/ connections there..also chech ground wires..all this is only if the battery does not have a shorted cell in it.. even new ones can get shorts..if you can get it to start go to autozone or advance..they do free testing..

What happens when you turn the key to on? Do the warning lights and gauges come on? Turning the key to start, do the lights and gauges stay on? Just nothing at the starter?

Or does power just shut off when you turn the key to start, everything goes out, no warning lights or gauges? Then check cables, battery terminals, grounds for clean tight connections. There is a problem between the battery and the ignition switch.

If the switch still receives and sends power out (to the dash, for one) but start circuit is not working (from battery to ignition switch to clutch switch to starter relay to starter solenoid to starter to ground-and back to battery), then here's where we at: with key off, use a small screwdriver and short the big cable at starter to the starter solenoid small wire connection, or use a small jumper wire to do the same-battery cable at starter to the small wire connection on the starter solenoid. Starter motor should spin and crank engine. Does it? If so, start checking the start wire out of ignition switch for power when key is held in start. If you have a clutch switch, check for power in with key in start. Should have battery voltage to the clutch switch with key held in start. Keep checking the start wire along the start circuit. Not sure how the start relay is wired into the circuit, would have to see a diagram, but if you pull the relay out and use a test light or multi meter, could check for power on the terminals where relay plugs in. Key off, should have one terminal that is hot. With key held in start, at least one other terminal should also be hot. This would be the start wire out of ignition switch sending a signal to the relay.
Good luck, hope you find it. Sorry I don't have a wiring diagram to help you more.

Check battery cable connections. There should be a hot wire (hot at all times) to the ignition switch, and when key is turned the switch sends power out. Either the switch has lost the power in, or the switch is bad, not sending power out.
Do the headlights work? When key is turned to on, do the warning lights and gauges come on in the dash? Does the radio or any accessories work when key is turned? If nothing works, you need to check if the ignition switch is getting power from the battery.

It sounds like a loose wire to the starter, check the wiring going to the starter for any corrosion, breaks and make sure all the bolts and nuts are tight.

this sound to me like at first I thought it was a fuse, as the problem went on it shifted more toward a weak cell in the battery, if a weak cell sits for a little while the battery will not hold the charge in that cell and that will cause loss of power, "its charge", in tne other cells. you had mentioned you used another battery and it ran great but when the battery was removed, things went wrong. You may check to see if there is water in your battery

tap starter while key is in start position. (need a helper) if it starts change the starter.

Check the connections at the battery. Be sure they're clean and tight.