its possible that the tumbler is "frozen" from "non-use" as most use a fob to open and close locks. Hence, depending on the climate area, the tumbler get crudded up and will not function. Pull the lock and sock / clean to see if it will function there after.
Try using something like THIS... BUT... After the Key Slides inside of the Lock-Work...Only make VERY SLIGHT TURNING efforts. If the Lock will NOT Yield... Try entering from the Passenger Door side next and once you get inside ...open the Driver's Side Door using the Door Handle and then... Manually work the INSIDE Lock-Unlock Mechanism to see if it will Break Free. This stuff ONLY lubricates the Tumbler... NOT all of the Inner Door Levers and Contact Bearings hidden under the Door Panel that ordinarily require treatments with Lubriplate Lithium Grease in certain spots.
I'd try using a rust penetrating oil in there first. Fill the lock with it and let it soak a good 15 minutes. Put some more in. Then, using the key, go back and forth to free it up. Try turning it. Put more oil, repeat a few times.
If you need to rekey or disassemble the lock, this is a good tutorial.
Thank you for the suggestions. I tried to loosen it up with some dry lube and then a little penetrating oil. In the end I removed the handle and disassembled the lock cylinder. Sure enough 4 of the blades didn't engage with the key I have. I ended up modifying the blades slightly so they work with my key.
Next on the agenda is having another key made.