screen freeze no bsod please help

Hi im new to the forum so please forgive me if this goes into the wrong area of the forum. There is a Summary and pc specs at the bottom if ive rambled on, i have recently decided to watercool my pc, i took my time as its my first watercool build but after finishing getting the loop set up and running then testing for 24hrs for leaks it was time to fire it up.
It fired up brilliantly no hiccups everything seemed to be running great but after 10 to 15 mins the screen froze on the webpage that i was looking at couldnt ctrl alt del, no mouse movement but the pc continued to run no beeping or strange noises and no lights on the motherboard.
ok so hard reset then went into the bios reset it saved and rebooted, again it ran for about 10 mins before freezing no bsod again.
so hard reset again but this time no signal to monitor and the ram led came on,turned it off removed the ram and inserted one stick at a time to see if it was bad, each time the pc turned on and was fine for anywhere between 2 and 10 mins the ram didnt seem to be bad so put it all back in and fired up.
It ran for an hour before freezing this time again hard reset but this time the boot device led came on so i turned it off unplugged and checked connections etc all seemed ok so i reset the cmos just incase and fired up again.
ran good for about 30 mins this time before the freeze, so i unplugged and removed the gpu so it would use the onboard graphics, fired it up and it seemed very unstable the screen was flickering and it lasted about 60s before freezing.
This time the ram led came on again so i switched to different ram and tested again but still with the freezing.
The screen freeze happens anywhere from 1 min to an hour no bsod or black screen with intermittent boot device and ram lights coming on.
i have tested all i can including the display port cable and monitor without changing parts as of yet so all im asking is any advice on what may be happening and which part to try first?
no leaks from the cooling loop and i have reseated the cpu and gpu waterblocks just incase and the cpu has been reseated the temps while running are stable around 20c so dont suspect overheating.
i have searched forums and the internet but everything from low psu power to bad gpu to even bad drivers keep coming up but cant find anything specific to screens freezing without bsod but as i dont know how long it will run software testing may not be an option.
System is as follows
asus z170i pro itx mobo
i7 6700k
corsair vengeance 2400mhz ram
asus strix 1070 gpu with ekwb strix waterblock
bitfenix 650 modular psu
samsung m2 ssd
1tb hard drive seagate
the cpu and gpu are watercooled using the ekwb slim 240 kit
not overclocked as of yet.
one magnetic led strip on the roof
2x 120mm corsair fans
1 x 140mm corsair fan
1 x 200mm phanteks case fan
Summary
new watercooled loop after installation getting screen/picture freeze no movement on screen no bsod
intermittent ram led and boot device led
runs for 1min to 60mins not overheating
still crashes when gpu unplugged to use onboard graphics
Any advice would be greatly appreciated thank you
dm740

first things first.. was the PC up and running before you water cooled it?

yes it was up and running for a few months before watercooling, and about a month when i swapped to the gtx1070 i did have a ram problem when i first installed the 1070 but a quick ram reseat and cmos reset and it was fine.

have you tried running memtest? also have enabled xmp setting on the ram?

pretty much trying to run anything results in it freezes even opening the bios with gpu installed and using the onboard gpu it just freezes before i can do anything unfortunately

try loosening off the cpu waterblock a tad (unless mounting has spring loaded fastenings).

have you had the CPU back out the socket while doing the water cooling?
if the above doesnt work I would be tempted to remove the CPU and check the pins in the socket.

when i first did the watercool the cpu stayed in the socket but i have since took it out checked and reseated everything looked normal and yes lude1962 the cpu block is on a spring fastner which i did slacken slightly when i reseated everything just incase it was a little tight.