Hi Sharon,
Firstly, read through the 'photorendering' section in the reference guide. The pdf version is found on the help menu within ArchiCAD.
In the rendering settings, select the 'Lightworks Rendering Engine' option at the top. Check you have the sun and ambient selected as light sources. Select 'lamps' also if you have lights on the floorplan. The 'sunobject' and 'skyobject' are also classed as lamps and need this setting to be on to work.
For individual lights - check the lightbulb buttons next to the slider in the individual light settings to see if the light is actually turned on.
It is worth checking the sun settings also to see if the right time of day has been selected. (It's under the 3d projection settings).
Hope that helps!