No video only command line

[Endie-157]

I have an iMac G3:
512 MB of ram,
500 MHz CPU,
Replaced the hard drive since the original didn't work
and the ATI Rage128 Ultra graphics card, being the source of the problems.

Followed all the instructions to get KDE working, with SDDM as the display manager, but neither will start.
But there is some stuff in dmesg that seems related:

aty128fb 0000:00:10.0: enabling device (0086 -> 0087)
aty128fb 0000:00:10.0: Invalid PCI ROM header signature: expecting 0xaa55, got 0x8181
aty128fb: ROM failed to map
aty128fb: BIOS not located, guessing timings.
aty128fb Rage128 TR Ultra AGP [chip rev 0x4]
16M 128-bit SDR SGRAM (1:1)
Console: switching to colour frame buffer device 128x48
fb0: ATY Rage128 frame buffer device on Rage128 TR Ultra AGP

Those seem to be the only lines related to the graphics card. Other than that it is perfectly functional from the command line, booting with grub if that detail helps.
Any help would be appreciated.

[kth5]

A bit more from X.org log would be useful.

Did you install the correct drivers (xf86-video-ati) and are they loaded?

Do you have an xorg.conf and/or what does Xorg -configure give you?

Does xf86-video-fbdev work if you force configure it?

I unfortunately do not have any pre-G4 hardware to test on. :(