Problem with new PC

[Koldsice]

Hello,
I bought a new PC recently(thanks to some of you here
But I have a recurring problem..
I bought a new CPU,motherboard,RAM and cooler,but the PSU,GPU and HDD and SSD are from my old PC.
I had a problem with my old build where the PC wouldn't turn on when I pressed the power button,only after a couple of tries and even then it took a minute or two.
Also the monitor would sometimes just go into sleep mode and then return (aside from going to power saving mode after 20 minutes or so),also a problem from my old PC.
Here are my full specs:
Msi z270a pro(new)
Intel i7 7700k @ 4.6(new)
Asus GeForce 1070(old but not even a year old)
2*8GB Kingston 2400 mhz RAM(new)
1*Samsung EVO 250 SSD(old)
2*HDD WD Black(old)
SeaSonic 750w X-series(old)
Fractal design define s(new)

Thanks to anyone who'll take the time!

 

[Kenton82]

Sounds like a possible PSU fault. I wouldnt have thought it would show up like this being a Seasonic though. Anyone else with a bit deeper knowledge than me have an opinion?