Sorry, I have no simple advice.
Normally I have in my Pegasos 2 gfx card Radeon 9800PRO.
But month ago I tested something on AmigaOS, so I changed card to Radeon 9000PRO. And this card also didn't work with MorphOS ( black screen or white screen). With OF and AmigaOS was fine.
I have now MorphOS 3.15. I am not sure, but I think that with some older MorphOS version it worked.
If you have another gfx card, try to change it.
AmigaOS3: Amiga 1200
AmigaOS4: Micro A1-C, AmigaOne XE, Pegasos II, Sam440ep, Sam440ep-flex, Sam460LE, AmigaOneX1000
MorphOS: Efika 5200b, Pegasos I, Sam460LE, Pegasos II, Powerbook G4, Mac Mini, iMac G5, Powermac G5 Quad
