You have inserted your ignition key into the lock, but it will not turn. Before you call a Professional Automotive Locksmith, there are several things to try. First make sure that it is not a locked steering wheel by turning the wheel from side to side while trying to gently turn the key. It may help to have someone else rock the steering wheel back and forth from left to right while you try to operate the lock.
If that does not work, insert some good solid silicone lubricant into the lock. WD40 will work in an emergency, but it has a solvent base and will dry the lock out after time. Do not use graphite unless you never wear clean clothes or keep your hands clean. I call graphite the black plague. After applying a generous amount of lubricant, insert the key and tap on it gently with the handle of a screwdriver. Caution must be used, especially if your key has a remote integrated into the head of it or a transponder inside.
If it is extremely cold, try blowing hot air into the lock with a hair dryer. You can also heat the tip of key with a lighter but be very careful not to touch the metal that you have just heated.
If none of the above works, it is time to call a professional automotive locksmith. If one is not available, you can have the car towed to a dealer or repair shop. If your car is a Ford, particularly a Focus, the lock has probably failed and needs replaced with one that will operate with your original key. If your vehicle was produced by Chrysler it may be possible to clean it after disassembling the lock, but I have found that this is a short-term cure and the problem will happen again. Replacement with a new lock is the proper solution. If you have a G.M.vehicle it may be possible to clean it out by flushing with a good cleaner, but replacement may be required if that does not work. Again, never replace a lock with one that does not operate with the original key. Most cars have transponders in the head of the key and reprogramming will be required. Your vehicle was designed to operate with only one key and that system should be maintained. Demand that your mechanic obtain a lock from a professional automotive locksmith or a new car dealer.
If you own a foreign vehicle produced by an Asian company like Honda or Toyota, demand that your lock be rebuilt by a professional automotive locksmith. Even if the lock must be replaced due to damage, demand that a professional automotive locksmith rekey the new lock to operate with the original lock.
Aftermarket locks sold by auto parts stores are generally not rekeyable nor of the same quality as the OEM lock. Sometimes they will carry locks produced by a OEM manufacturer, but they will need to be rekeyed. Dr Auto Lock only uses locks that are manufactured by the OEM supplier. Demand only the best parts be used in the repair of your vehicle. Inferior locks cost more in the long run and that is a fact.