I had the same problem. Iam building the new PC, all parts are new, which is

1) CPU i7-7700K 

2) Cooler TX3 EVO

3) H270 Pro 4

4) CORSAIR DDR$, 4GB*2, "$, 2400 (https://www.amazon.co.jp/gp/product/B019HVND88/ref=oh_aui_detailpage_o00_s00?ie=UTF8&psc=1). This RAM is compatible with the motherboard. 

5) PSU ENERMAX EVOLUTION DUO 700W (http://www.enermax.com/home.php?fn=eng/product_a1_1_1&lv0=1&lv1=99&no=335)

6) Western Digital Green 240GB (https://www.amazon.co.jp/gp/product/B01MDM3WI5/ref=oh_aui_detailpage_o02_s00?ie=UTF8&psc=1)

7) GPU Palit 1080Ti Super Jetstream (http://www.palit.com/palit/vgapro.php?id=2859)

8) Case: Corsair superior (https://www.amazon.co.jp/gp/product/B06XS364S8/ref=oh_aui_detailpage_o01_s00?ie=UTF8&psc=1)

Here is some pictures of my setup: https://photos.app.goo.gl/L7uOhafkmMcfo1FA3

As the case of Ralph.B, I followed every step to assembling it and it think it is right. When I hit the power button, all the fans (cooler fan + chasis fan+GPU ) operates properly, but there was no signal to screen. I also tried without GPU, using onboard VGA, HDMI, DVI, but the result was the same. 

I tried to other several monitors but still the same. The monitors work well with other computers. 

Here is what I tried:

- Reassemble from the beginning

- Take out CMOS battery, leave it for hours and then put it back

- I checked:

- CPU pins are good

- 8pin and 24pin power cable plugs well to the motherboard

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Other problem is sometimes I press power button at the chassis but the PSU did not run. I plug out its power cable, leave it for a while, then plug it in, it then worked again.

But even it worked, sometimes, I powered the computer on, the computer run for 5-6 seconds and then it automatically powered off. But that is "sometimes", not all the time. I could not understand the reason. Maybe it is due to overheating ? or problem with the PSU?. 

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I tried many ways but still no hope so far. Please help. 

Thank you very much. 

To Ralph.B: You said  "The CPU and CHA fan cables were switched. Whoops. Problem solved."

Do you mean that the cooler cable should connect not to CPU fan but connect to the chassis fan plug in the motherboard? I tried but still the same

EDIT: The CPU and CHA fan cables were switched. Whoops. Problem solved.

Everything is plugged in right. When I hit the power all of the fans and lights go on, including the GPU lights, but it doesn't send any video to the display. We tried taking out the video card and using the onboard graphics (VGA and HDMI) and both yielded the same result. The monitor itself works with other devices. I reset the CMOS using a jumper but nothing changed. I've unplugged everything and plugged it back in. I've considered taking out the CPU to make sure the thermal paste was applied correctly as I wasn't there at the time the computer was put together.

Core i5 7600

Asrock H270M pro4

Gskill F4-2400C15Q-32GRK

no video card installed

Seagate HDD

Memory full model number is Kingston HX424C15FBK2/16. Tried different combinations, and of course with no modules inserted at all. So it's not the case.

Dedicated GPU was attached just to check fan power. Tried starting up using integrated with DVI and HDMI slots.

be sure to clear the CMOS/BIOS before starting the PC again. - this is what I forgot to do.
Will try to assemble everything step by step with all precautions, hope I've just made a little stupid mistake last time.

Anyway, thanks for your reply!