Pc don't starts

[Huzaifa_6]

Hi, so I have this kinda low end motherboard (it's hp's don't know the exact model), the problem is that my old graphics card was not working so I recently bought Rx550 gigabyte 2gb, and it had windows 8 but the card wanted win10 so I upgraded to Windows 10 64bit but the thing is that since that time my is not starting, the led on psu is on I thought my power button is broken so I tried to start manually from the motherboard but it did not, I put back the power button connector in it and it started, there was absolutely no problem after it started it kept playing video games and when I tried to turn it on after shutting it down it happened again and this time it took like 3 hours before it started after pressing the button, I don't know what is the problem here please help me

 

[Huzaifa_6]

Is there anyone that can helps me?