My 08 sport was left in car park for a few hours. On return the car would not open by the key?No hazard lights appeared when pressing key fob? So thinking it must be key battery returned to car with spare key (never been used) and this also did not work so what could be the problem please?

Quit SHOUTING will ya :>D Typing in all CAPS is considered SHOUTING in Internet land. It also make the text VERY HARD TO READ.

You need a good, local auto electrician with a pro-grade scan tool computer. You have a faulty module probably Body Control Module, or Security System Module, the sensors and receivers connected to them, or a general communication issue.

Insert key into and remove it from ignition more than six times in 10 seconds. When the hazards lights will flash twice insert key into ignition and turn to ACC position.
Then push any button on key fob once, the hazard lights will flash twice. Then open drivers door to END.
Should be all working again.

Not without knowing the year, make, model. Electrical is different in every vehicle

You have to take it and get it reprogram. The pcm is not able to remember it.

You are going to need to check the power lock control moduel on the inside of the door panel. If the FOB appears to be working but the doors are not unlocking, you need to check this. I would also replace all fuses that control the locks. If both of these devices check out ok, you may need to replace your FOB. To check your power lock control moduel, manually lock and unlock your doors by pressing the lock button on the inside of the door. If it does not work, it is either the fuses or the power lock control moduel. If it works, your FOB has gone bad. Hope this helps! Please rate 4 thumbs up!

You should be able to just unlock the door with the key, and even if the alarm is still going of try to start it the key should override the alarm.

replace batteries in remotes,then with key unlock car/hold key over windows go down,wait 20 secs,then lock/hold key over,windows go up,wait 20secs, then using remote press/hold down the unlock button for 30 secs.you have just reset the alarm/immobiliser.if remotes/keys dont work after this,then take it to a dealer for a computer/key reset.

sounds like the security part of the system went bad
take the key fob to the dealer and have it reflashed
if that fails replace the security computer or you can disconnect it from the car you won't have the system but the hazards won't come on unless you turn them on

Horn problem is either bad horns or failed clockspring behind steering wheel which is the connection for the airbag and horn buttons.

If it is a 2003 model year vehicle follow this procedure. If it doesn't work, you may have the wrong fob which happens all the time.

Sit in vehicle and close all doors.
COMPLETELY insert and remove ignition key more than six times within 10 seconds.
Hazard lights should flash twice.
Turn ignition to ACC position
Press and hold any button on the new key fob hazard lights will flash twice
For a second key fob using the master lock switch, lock and unlock the doors then hold down any button on the second remote until the hazard lamps flash twice.
Then you are done open the door to exit the programming mode.
If the lamps didn't flash when holding down the key fob make sure you have the right key fob, they are different for each car.