Sony dsc h5

i m having problem with the AF illuminator light. the problem seems to be either with the shoot button or with the af illuminator light. when i press the shoot button half way, i expect the af illuminator to light up, and the auto focus lock indicator to appear and beap when it is locked to the image. This is not happening.
It only works, when i press the shoot button full way down, the camera focuses itself on the image, but it is not the way i want it to be.

Thanks for the assistance whenever it comes wherever it comes from.

Cheers!!