Just clicks when trying to start. New battery, new starter and new generator. This problem has been happening intermittently. Cannot predict when or why.

 

Verify that it is the specific starter relay that does or doesn't click . With the key in the on position only do the same with the king relays circled in red in the fuse boxes . One person test you can pull the relays from their socket and feel them to click as you have the key to on but not for the starter relay as it is a spring loaded key start contact .

 

I've had a similar problem. I would turn the key to the ignition position but would only hear a click on the passenger's footwell. It was a faulty inertia switch. You might want to check that.
*Push down on the button on the inertia switch (even if it is not in the up position), then retry turn the key over.

 

If the car doesn't respond to either of the suggestions above, I would start checking earths under the bonnet.
1. Is the main battery power cable running from the trunk to under the hood, it terminates around the brake servo housing, and is connected to a brass nut and bolt...remove and clean.
2. Opposite side, you'll see 2 fuse boxes, a large and a small, the link lead between joins both and has ring terminals, remove the nuts and clean both rings and posts.
3. Engine earth, under the car passenger side, back of the bell housing to chassis, looks like a battery strap, again remove and lean the ends and reinstall.

I'll bet it's one of these.

Hope this helps