It sounds like the steering wheel is locked, try to wiggle the wheel at the same time you turn the key.
I went to a lock shop that specialized in keyless entry. They sold me a Fob for $70.00 because i didn't have one & they programmed it.
It doesn't use the car key. There is a special key. Mine was in the glove compartment. You may have to call the Buick dealership in your area if you don't have the special key. (Mine was made of green plastic).
The key fob battery in an 02 Buick Rendezvous is changed by prying the case open using a coin or screwdriver. The battery can then be pulled out and a new battery installed.
Put the key in and move the steering wheel until the key can turn
If you have the key and it won't turn the lock cylinder try jiggling the steering wheel while turning the key. If the steering wheel lock is merely jammed that should loosen it enough to turn the key. On the other hand if you don't have the key or the lock itself is jammed you may want to replace the lock cylinder.
Jiggle the steering wheel as you turn the key. I've owned several cars in which the steering wheel lock wouldn't let the key turn if there was any pressure on the steering wheel lock.
Yes, a good mechanic should have the tools to remove a wheel lock without damage to the wheel.
check your battery connection, your key will lock down if the battery is low or it is not grounded, no power will lock it in the slot
On the GM cars I've worked on, you have to remove the steering wheel. There is a vertical retaining bold/pin that has to be remove to allow the tumbler/key lock cylindar. Remove the wheel. Remove the retaining pin. Then remove the tumbler. Reverse the above to install the new one. Hope that helps.
Remove the steering wheel and lock plate then the turn signal switch and key reminder contacts, then a screw that runs right against the lock cylinder and pull it out. You need a puller for the steeering wheel and a spring compressor fot the lock plate available to rent at most parts stores,
The wheel should lock when you take the key out of the ignition. If it doesn't, there's something wrong.