My chuck key on my Ryobi Cordless drill/Saw Combo, is stuck in the fully opened position and will not tighten at all. Was working for a while then just happened. Thanks ahead of time.

'make model (what it is)' as first three words of every question please.

All the ways to tighten a drill chuck in the link. I have one with a key and my cordless drill has a central position between forward and reverse that locks the chuck.

https://www.google.com/search?q=tighten+the+drill+chuck

..

easy to fix
with the drill not running

grab the bottom part of the spinning part of the drill nearest the drill's motor.
then
grab the spinning shaft bit nearest the drill bit
pull them apart slightly

when the two parts are pushed together thay lock the chuck

I own a ryobi hammer drill that does the same thing

Try holding the bit in a vice and gently tap the chuck off of the bit and see it it releases the pressure on the jaws.

Put the biggest hex key you have in the chuck and tighten it then hit it clockwise with the spindle lock engaged a couple of times. The screw in the chuck will then undo clockwise and the chuck can be undone after by putting the allen key back in and unscrewing it anti-clockwise maybe with a light tap from a mallet.
Hope this helps
Jon

Abrupt stops can loosen the ratcheting chucks. Before the invention of those chucks we had the ones that required a key. The proper way to tighten them is to alternate between all three position in order to "seat" the jaws on the bit evenly.That all but guaranteed it would not come loose I assume you have a ratcheting "one handed chuck". ther's only one way to tighten them and you don't get the same grabbing force. The only thing I can suggest is to try to eliminate abrupt stops or try cranking it tighter.

The battery isn't any good. The charger is just going through it's regular steps. (I know how it is. I just bought two Ryobi 18 volt batteries for my Ryobi cordless drill, reciprocating saw, flashlight,
trim circular saw, combo set. $60 for two batteries)

I would replace the chuck or purchase a 1/16" quick change drill bit.

according to my breakdown its a drill. do you checked if there is a screw inside the chuck. if there is one remove it by turning clockwise.open the chuck fully & insert allen key 5/16 or 3/8 short side to the chuck.tighten the chuck & wak the allen key with a hammer counter clockwise. do it again if required.putting back together the other way.

After removing the screw and inserting the allen wrench shift the drill to the LOW position and turn the clutch to the drill only position. Use an allen wrench about the size of the chuck capacity so that it will not flex when hitting it with a mallet. Sometimes they are stubborn because of the torque but this should work. Put the allen wrench at about a 30deg angle and hit the wrench. I support the chuck on a workbench or a block of wood will do fine. The chuck has standard threads.