The fact its seeing 2 laptops is due to the optimus.
IF you do not get any screen out of the box while very unlikely it sounds like you have backscreen issue especially since you said you can see it if you shine direct light to it. If it was the cable then you wouldn't see anything at all but who knows, it could have been the cable.
Its annoying to be dealt with since its a new laptop but trying to see if its the cable or not it would save you a lot of hussle since you can get a new one for pennies and replacement is pretty easy.
If would recommend to try and see if its the cable as it won't void your warranty and if you found out it is the cable indeed unless you're really anti tech savvy I'd advise you replace it yourself as otherwise you'll be without a laptop for week or even longer, unless they give you a brand new unit.
Asus Rog G750JZ
Screen: 1920x1080 17.3'
CPU: Intel® Core™ i7-4700HQ (3.4Ghz @ -70mV)
GPU: GeForce GTX 880M 4GB (OC +125Mhz Core, +600Mhz Memory @ 1.062V)
RAM: Samsung 32GB 1600MHz
Storage #1: Samsung Evo 840 250GB
Storage #2: Samsung Evo 850 500GB
Storage #3: Seagate Barracuda 2TB
Storage #4: Samsung Evo 128GB MicroSD