2006 colorado intermittently fails to start. It

You can't. The security system and immobilizer is there to stop EXACTLY what you are trying to do, start the car without the key and security code credentials.

Your local dealership with make you a key based on the VIN Number. Then you have to reset the security system.

Or you can try a local mobile locksmith.

Or find the key. If you lost the key in the snow, look up 'Ring Finders', a global network of metal detectorists that find lost rings and keys.

everything you mention indicates a failing starter motor. Pull it and have it bench tested by an accredited auto electrician as they can be repaired if the failure is not to bad.

put gas line antifreeze.

Do you have a security light flashing in the dash when you try to start it, does the starter spin the engine for but not start it up? Have you tried spraying fuel into the intake during cranking? Do you have spark? Any fault codes? All this can be the problem and other things as well, have them all eliminated as the cause.

How often is this happening? Did you hear the alarm go off? Do you have an aftermarket radio?

does the unit crank after it fails? I would check all of my battery connections you may have a loose ground either at the battery or at the engine. You may also have a bad starter relay located un the fuse panel under the hood

Sounds like a bad battery. A number of chain auto parts stores will check it and your charging system free. Before that, if your battery has removable caps, check the water level, if it's down, fill to the bottom of the fill rings and charge the battery, if you have a battery hydrometer, all the cells should have about the same charge level, if one or more show a lot lower than the others, battery is probably bad. Hope this helps.

Your Main Battery is Flat, get a jump start if its safe or remove the battery and hook it up to a charger. Maybe you left your lights on, or your alternator isnt charging the battery properly when your driving around. Sometimes this can be the bushes located in the alternator.

Start by checking GM Technical Service Bulletins

Lots of issues on most Colorado's

Define "won't start." Do you mean the starter motor won't crank the engine? Engine cranks but won't fire up? Fires up but dies?