Question Interesting issue with PC not posting but only when first plugged in.

Oct 30, 2020
I have just put together a PC for my cousin using various parts out of other PC's, but I am having a continuous issue with the computer not powering up... So, when I plug in the PC and turn on the power supply, lights on the MB and GPU light up, but when I proceed to press the power button, nothing happens. I can only get it to post once I have turned it off at the PSU, waited until the MB and GPU lights dim, then plug it in an turn it on. After this is done I can turn it on and off at the power button as many times as I like, but as soon as it is turned off at the PSU it is back to square one. Also it may be worth noting that when it first boots, it stops at a status screen, which I have to manually choose this startup disk (this only happens on the first bootup though). Very occasionally I will get a CPU fan error on the status screen (and 1 long beep followed by 4 short from the buzzer).
What is the likely cause of this, and how can I go about fixing it?

  • Asus Z77 Sabretooth MB
  • i7 4790k CPU
  • ROG Strix 1050ti GPU
  • EVGA 650GQ PSU
  • 2x DDR3-1866 HyperX 8GB
Thanks in anticipation.