Gpu stopped working now no gpu will work

[plinkity]

About a month ago i bought a rx550 4 Gb and at first it worked fine. I got home one day and there was nothing on my monitor but the rest of my pc was still running, audio etc.. I restarted and then it wouldnt boot with the gpu in, the mobo beeped five times. I took it out removed the cmos battert and now it boots and runs fine without the gpu. I took the rx550 back to my store. Turns out it was broken so i got a replacement and upon returning got 5 beeps yet again.
I tried both pci e slots with both cards and got the same results.
How do i know whats wrong with my pc?

Im running asrock fata1ty h87 atx mobo
Intel i7 4770 cpu
16gb crucial 1600 ddr3 ram (2 x 8gb)
A raider ra550 psu, i dont thunk it had the 80+

I reseated everything bar the cpu and used a multimeter on the leads coming from the psu, the 3.3 5 and 12 voltages seem stable while running.
I bought this setup 5 years ago and just want to play fortnite at a stable 60fps+ please advise! Thank you

 

[dontlistentome]

Make sure it's in the correct pci-ex slot. Also, I'd check the motherboard bios. If there is some kind of compatibility option in there you might want to try it. And there might also be a 'secure boot' type of security enabled, that can prevent adding a videocard so you might want to disable it until after the card is working.

Lastly, if you already got one defective card from this place how do you know this second card works? An RX 550 or GT 1030 are not good choices for 60fps+ gaming at 1080p on games like Fortnite. You have an i7, I'd go for at least an RX 460/560 or GTX 1050.