Right, first things first. You will need to remove the door card to access the solenoid inside. There will be 3 screws on show that you will have to remove to be able to take the door panel off. The first screw is inside the door pull, the second is under the speaker cover (just use a flat head screwdriver to GENTLY leaver out the speaker cover), and the third is were the door card meats the interior (kinda under the wing mirror but inside the car). Once you have removed all 3 screws the panel will be held on by plastic clips. Use your finger or a screwdriver to GENTLY leaver at each point of the clip. Do this very carefully as they a very delicate and can snap very easily.
The top part of the door card is held on by a seal kinda thing by the window. When all the clips are undone pull the door card up towards the top of the door. With a bit of wiggling the door card should finally come free!
When this is off there will be an insulating cover that hides the gap you will need to use to access the solenoid. Gently unpeel this and look for a little black box with a white top surrounded in rubber. (This should move up and down). When you have found this little black box, feel the white top and press the key fob. This should move up and down. If it doesn't that will be your problem.
To put back together just push the protective cover in place, clip on the door panel and screw back in place.
Hope this helps, Good luck!!!!