Asus Hardware Component Failure noise

###Build Help Hi Ive just been building my first PC and i went all out on the rig but when it came to building it i followed all instructions and built it right ( I Think) and when I powered it on I got 1 long beep and then 4 short ones from the motherboard. This supposedly means a hardware failure and i cant narrow it down.

I'm really hoping there isn't a hardware problem and I've missed something but I just wanted some help in understanding whats going on.

Specs: MB: Asus Maximus VIII Hero CPU: Intel i7 6700k RAM: HyperX FURY 16GB DDR4 2400MHz PSU: EVGA Supernova 750W Gold HDD: Seagate 4TB SSHD M.2: Samsung 950 PRO NVMe 256GB Monitor: BenQ XL2430T Case: NZXT Phantom GPU: MSI NVIDIA GTX 1080 Founders

I have a BD drive and an NH-D15 but I didn't think they could have affected anything.

The GPU is not installed but everything else is. I've tried methodically taking parts out and trying to boot it but the same issue occurs. Do I NEED the GPU before it will boot?

Otherwise, I can only assume its the motherboard or the CPU and since the MB is functioning properly lights and all I think it must be the CPU. Am I right there and have to change parts or have I missed a compatability issue? Any help would be appreciated!!