I take it you checked for jumpers and without any extra parts. That is, one stick of RAM, no drives, etc.
As to jumpers, a funny error was the manual showed a HDD LED connection and it was actually a sleep jumper so half the time the machine power up, beep but nothing more. REDUCE THE MACHINE to just a few parts. You don't need more than the Power On connection and speaker, the mainboard, PSU, CPU+HSF and a stick of RAM. You don't even need a case.
Many builders start with all parts. Trouble follows.
I have built a custom water cooled pc only to find that when I turn it on, the motherboard does one short beep. I have no idea what is wrong and I need help. I took out the graphics card hoping that it would work, only to find that there was still the same beep. None of the system fans work when I power it on. I know that the motherboard, power supply, fans, cpu and RAM all work so please help me with what is wrong. I am going to provide a link with photos and a list of the parts I used.
Asus Maximus VIII Hero
Gigabyte GTX 1080 Founders Edition
Kingston HyperX Fury
Fractal Design Define S
Samsung Evo 850 1tb
2 Western Blue Digital 1TB
I apologize in advance that there is no graphics card in the photos