Stuck on start up

I bought a used iBook (PowerPC G4 1.33ghz 12 "), when I try to turn it on the Apple logo comes out (it has white stripes) and it gets stuck in the loading in a blue screen. I tried all the key combinations but it doesn't work, only safe mode works. I tried to repair the disk permissions in Disk Utility (not in recovery mode), I also tried to use the Apple Hardware Test disk but it remains stuck in the frame. I tried to remove the additional ram and the keyboard but nothing. Maybe it's the GPU?