I was trying to install Debian with a newer version, but that was no success at all.

...ok
opening display /pci@0,f0000000/ATY.WhelkParent@10/ATY,Whelk_B@1 ... ok
copying OF device tree ... done
starting cpu /cpus/PowerPC,G5 ... failed: 00000000
Initializing fake screen: ATY,Whelk_A
Calling quiesce...
returning 0x01400000 from prom_init

…and then silence. Well, not completely, because the fans start blowing after some time… And they can get really loud indeed!