1999 alero ignition key will not turn, seems like lock is worn tried spare key no help ,last evening was fine. happened 2 months ago then poof started working 2 hrs later

rough guess is that the battery is faulty
have a load test done on it
cold weather kills failing batteries quickly

sound like theft security problem.when you try ten minutes did you leave ignition switch on position for ten minutes until the security light turn off then turn off ignition switch for 5 seconds then try starting vechicle.when you do 10 minute trick security light has to turn off or disappear when you see security light go off turn off switch 5 seconds then try starting vechicle.

sounds like either the key or the lock cylinder is worn out
if you have a spare key try it
if it wont turn it you need a new lock cylinder with new keys

it has to be programmed for the immobilisor to be turned off so vehicle can start ,i would call a auto locksmith to sort out this problem for you as i have a funny feeling that you have lost the chip out of the original key

I know it sounds a bit silly, but have you tried jiggling the key? ... that MIGHT help (it worked in my 95 Corolla when the same issue happened). If you have another key available (one that is not used as much) that could work too ... sometimes the key itself wears down, so the key does not fully depress all of the locking cylinders in the ignition. In other words, if the key is used a lot, it might be too worn out to work right, in which case you can get a new key and it should work just fine (this is what had happened in my 95 corolla)
If this is not working, and even with a less worn out key, the key is still locked in the "Lock" position, try turning the steering wheel back and forth a bit as you are turning the key. There is a safety mechanism in Toyotas that prevents the car from being used without the key (prevent hot-wiring) ... If the key is out of the ignition, and you turn the wheel, it locks up the ignition switch and the steering wheel of the car. Sometimes this mechanism gets stuck as well, and keeps you from being able to start your car. Moving the steering wheel back and forth as much as it will allow (usually only a couple of inches) should help to unlock your ignition and get you on your way.
Finally ... the locking mechanism of the ignition switch (what I was talking about in the last paragraph) sometimes breaks, and causes your car to remain locked, no matter what you do. In this case, you will need to go to a mechanic and replace the key / lock unit. It is not terribly expensive to have this done, but it means replacing all of your keys and spares ... DON'T FORGET TO REPLACE THE SPARES, TOO if you are going to go this route.

keys & locks are subject to wear,especially if you have a large or heavy key-ring.do you have a spare key to try?the tip[pointy end] of the key is what releases the lock.have a new key made.if that doesn't work,call lock smiths for price to replace lock cylinder.

HAVE YOUR CAR HOOK UP TO A DIAGNOSTIC SCANNER TO SEE WHAT CAUSING THE CHECK ENGINE LIGHT TO COME ON.IF YOU ARE HAVING SECURITY PROBLEMS THE DEALERSHIP HAS TO FIX IT.SOME TIMES YOUR IGNITION KEY OR LOCK CYLINDER IS WORN WHERE THE BCM AND PCM DONT RECOGNIZE IT.THINKING ITS A THEFT CAUSING CAR TO SHUT OFF.SEE THE DEALERSHIP HAS TO SEE IF YOUR KEYS IS WORN TO A POINT WHERE THE BCM AND PCM.DONT RECOGNIZE. THE IGNITION KEYS.SO THEY HAVE TO REPLACE THE KEYS ALSO IGNITION SWITCH AND BCM.THEN THEY HAVE TO REPROGRAM THE NEW KEYS AND IGNITION AND BCM TO THE PCM SO THE CAR WILL CRANK UP.THIS IS A DEALERSHIP FIX.

The keys on this vehicle have a problem with wearing down to the point where it's a pain to get them to work in the ignition cylinder. Examine your keys for wear and that may have been your problem since day one.
I have a 2004 Vue and I have the only key I got with it (used car) worn down to the point where it will no longer work in the back door and is a pain to use in the ignition cylinder. It also falls right out of the ignition cylinder when the car is running. I have a copy of the key that was made when I got the car which works just fine and doesn't fall out, and looking at the two side by side, you can see that Saturn's key has worn down substantially since I got it two years ago.

2 things either your switch is wore out and needs replaced or the cable from park to your switch is wore out and need to be replaced could be fixed easily at a small shop even shouldnt cost over a 100.00 for both to be replaced.

that's probably just bad spares. try going to a different store to have them cut (hardware stores are a good place to go) or you could go to a gm dealer too.