Question Freezing / no signal screen while booting

[Er190]

So I tried to bulid new pc:
Asus z270-a prime
I7-6700
Gtx 750ti
Psu- Modecom 500 W

While booting up computer that what will happen is random. One time its just freezing at asus logo on start without nothing... Just asus logo. Other time its no signal and screen becomes black. Rarly I can enter bios but in "Easy mode" in bios i can be for like max 10 s and screen freezes. When I quickly enter "Advanced mode" I can stay for 3-4 minutes. But as I said thats happen rarely. I tried booting with 1 ram , withot hdd ...etc. Then I thought it was a psu problem so i changed it to 450 W friends psu but same problem. I changed ram... Same problem. Time began for cpu so i went to my friends house with my cpu... And same situation on his computer.
B150 msi gaming mothwrboard
600W psu
W/o. Graphics card
So i knew that was cpu problem. The strangest part becomes here.
Psu was used in my older cimputer as well as box cooler and hdd disc. Motherboard was bought new and cpu was bought used from other friend who used :
Chieftec 750 W
4 x 8gb hyperx 2133mhz
B250m-d3h gigabyte motherboard
And when we used cpu on my other friends computer (this what i bought cpu) it was working properly. I have no idea what the problem is.
Maybe you know the solution?

 

[Lutfij]

All the PSU's you're mentioning in this thread are either fire starters or fire crackers. They shouldn't be anywhere near a computer or a PC component. You should look into a reliably built unit(borrowed from a friend or neighbor) and see if the issues go away, and if the system isn't damaged.

 

[Er190]

All the PSU's you're mentioning in this thread are either fire starters or fire crackers. They shouldn't be anywhere near a computer or a PC component. You should look into a reliably built unit(borrowed from a friend or neighbor) and see if the issues go away, and if the system isn't damaged.

... So you're saying thats the PSU problem? Why?
What PSU do you recommend then?

 

[Er190]

I'd like to add that on motherboard I have 4 lights each for cpu, ram, vga and boot.
When screen turns black at beginning vga led stay lit. In any other case boot led stays light up. Cpu led and ram led are only lit for half a sec at the beginning of turning on computer.