You need to restart
After a few seconds from start up a black rectangle appears with the message in four languages: " You need to restart your computer. Hold down ..." By firewire target mode I checked the status of the HD by Disk Utility and all it is OK. I tested the hardware by the Apple Hardware Test and also in this case all components were passed. Then, I reinstalled the OS 10.4.11 by firewire target mode but nothing changed. When booting in verbose mode, the last two lines are:
"Darwin Kernel Version 8.0.0: Sat Mar 26 14:15:22 PST 2005; root:xnu-792.obj-1/RELEASE_PPC
panic: We are hanging here....