PC Processors

[cincinnatux]

I have a new PC build with name-brand parts and when I have my new Radeon 5900 XT GPU installed the computer POSTs fine but the display remains black. I've used 2 different monitors (one using DP, one using HDMI) with the same result for both.

The first time I booted it actually worked. I logged into Windows and went to manually install the Radeon driver, but before I could get the AMD Website to load into Chrome, the screen went black and has never recovered. 

I put my old GPU (a GTX 1070ti) into the PC and it runs fine doing that. The problem is that because the build is a mini-DTX build any time I change ANY component it involves disassembling most of the PC. Popping the RAM out, for example, is a 20-minute endeavor. 

My x570i motherboard provides a POST code of 'AA' (pass all tests). I've confirmed that the computer works with this exact same configuration but an older graphics card. 

My power supply may be a problem - it is only 750W (Corsair SF750) and AMD recommends 850W minimum, but it should still boot up, right? I wouldn't expect wattage to be an issue until it actually attempts to draw more power than the computer has to offer, and surely showing the AMD logo during boot shouldn't strain it, you know?

Any suggestions for how to troubleshoot this further?

[cincinnatux]

UPDATE: I keep rebooting the system every half hour or so for poops and giggles and suddenly it output display. I quickly hit F2 to get into the BIOS settings and I disabled D.O.C.P. on the off-chance that the RAM was failing somewhere and saved and rebooted and this time the system came up and I installed Adrenaline and used that to install the AMD video driver. So far so good, I guess. 

Anyone know if RAM issues alone could explain the problem I was having? I don't understand how the RAM could pass the POST test but still prevent the video card from outputting video signal. 

I'm afraid to reboot the system now for fear it will go dark again.....