Mitsubishi Repair: Door lock mechanism, magna solara, silicone lubricant

Question
Hi, I just bought a second hand '98 Magna Solara, and all of a sudden both door locks are stuck tight. The key goes into to the tumbler but the tumbler won't turn.  It's an issue as I can't lock my car up properly at all. I've been leaving one of the rear doors open to access the vehicle but it's not the safest solution to my problem.  The boot opens with the jey with alot of key jiggling, but its not practical. Key starts ignition no problem. Any advice would be greatly appreciated.  

Thanks

Answer
Gus,
You may just have rusted key tumblers.  You should spraying a silicone lubricant or WD-40 into the tumblers and slowly work the key in it by turning back and forth.  If that does not help the problem, you may required getting the locking system inspect and serviced by a mechanic.
Good luck!