I am new to QGIS and working with QGIS 1.7.3 version, I have my all layers in WGS 84 CRS but even though they are not overlapping to each other, What should I do ?
It's difficult to tell what is being asked here. This question is ambiguous, vague, incomplete, overly broad, or rhetorical and cannot be reasonably answered in its current form. For help clarifying this question so that it can be reopened, see the FAQ.
My first guess would be that the spatial references are not correct or may be missing. If you have a layer that you know is correct (i.e. other layers overlap) then take an incorrect layer and try to reproject using the coordinate system from a correct layer. This walk-through may be of some use to you.