Need help with pc build random shutdowns

[ShootHappens]

So my friend and I built a pc in February, which consisted of 

Ryzen 5 3600
Enermax 360 liquidcooler
Crucial balistic 16 gb 3000mhz
Samsung 960 evo SSD, 1TB
Kingston a2000 m.2 1TB
Asus X570-prime 
PowerColor RX5700XT
Coolermaster 750 80+ Gold

The problem we are now having is that sometimes at random times the whole pc just shuts off and reboots. We have tried reinstalling windows, new drivers, old drivers, having it all taken out and built it from scratch. Checked cables, with build in graphics only, etc. And it still happens. Sometimes after minutes other times after hours. Really need help with this since he is pretty much ready to throw in the towel. 

Any ideas? 

[jaslion]

How are the temps during heavy usage (after 15minutes because ya know water in watercooler needs to heat up). Wouldn't be too suprising if that is the issue as all enermax aio's have a issue with slime that basically makes them useless for cooling.

[ShootHappens]

3 minutes ago, jaslion said:

How are the temps during heavy usage (after 15minutes because ya know water in watercooler needs to heat up). Wouldn't be too suprising if that is the issue as all enermax aio's have a issue with slime that basically makes them useless for cooling.

Ahh. Ehm I'm not too sure. But at load it doesnt come up over 75c 

[jaslion]

1 minute ago, ShootHappens said:

Ahh. Ehm I'm not too sure. But at load it doesnt come up over 75c 

Well test it with running something like cinebench for it's 10min temp test or something but a couple times.

[ShootHappens]

6 hours ago, jaslion said:

Well test it with running something like cinebench for it's 10min temp test or something but a couple times.

I don't think he can. Right now it's shuts down a lot 

[ShootHappens]

5 hours ago, WikiForce said:

have you tried swapping PSU?

Not yet. But it's completely new 750 gold Coolermaster psu