Powerbook G4 1.5 FW400 - blue screen, black screen

Hi, my powerbook g4 a few days ago display blue screen, I installed a fresh copy of osx, the install is done but at the boot after the gong the powerbook display a blue screen, only in security mode OSX run correctly. Yesterday searching on the web I found the commands for resetting pram and similar, but nothing works. At some point I pressed a combo of keys and the powerbook has restarted but the screen is always black and I hear the gong at the boot and the music at the first run of osx after the new installation. I don't remember the combo of keys that I pressed.

Anyone can help me?

Thanks a lot.

Leonardo