RX580 black screen after boot sequence: high Sierra, Mojave, Mojave install disk

Hi there,

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I'm running out of options, so I have to ask for other input.

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I had a Mojave system running for about a month and a half. RX580 in it, all good, didn't mess with any other hardware, didn't change anything other than upgrading to 10.14.4, and then re-applying audio kexts with KextBeast or whatever the utility is.

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Then after a forced reboot (power failure, backup battery was dead - swapped batteries since), my two screens would go blank after it got through the initial boot sequence (either verbose or just the apple logo and loading bar). The system is up, it runs services as it should, I can ssh into it, I can access shares.

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What I cannot do is:

• get a cursor
• remote screen into it (it's active)
• use teamviewer to connect to it (also active, appears online)
• use anydesk to connect to it (also appears online)

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What I have tried:

• replace initial RX580
  • I plugged it into another PC, and the same behavior ensued, however after about 4 reboots that card didn't even display BIOS and eventually the PC stopped posting. Bad card.
  • this replacement RX580 behaves as the first one did before it completely failed
• boot to a Mojave installer
  • same behavior: black screen, no cursor past boot/load sequence
• safe mode
  • fails, gives me an X
• singe user mode
  • boots fine, presents working console. When I type exit it loads the system to the same: no cursor, black screens
• boot without RX580 plugged in
  • system works normally, UI fully responsive, no issues whatsoever
• mess with gfx settings in BIOS
  • no change
• boot High Sierra (previous SSD)
  • system boots, I can see shares, can ssh into, cannot start remote screen control via macOS, teamviewer, anydesk. Does not have a mouse cursor
  • this made me doubt Mojave and now I'm thinking maybe the motherboard is toast or at least the PCI slot

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What else do you recommend I try? Thanks!