Among all the MacOS X releases, 10.5 (leopard) is definitively not the most stable. It’s getting better update after update though. In my experience 10.3.x was the most stable.

If for some reasons you get the infamous grey screen which last for ever during the boot, or if the mac keeps on doing loops during the boot, here a solution to your problem by booting in single user mode.

1- reboot the system or force reboot the system if it is stuck by pressing : ctrl+apple+start button

2- immediately after the starting chime, press and hold apple+s

The mac will start in a single user mode which is just a hoardcore unix terminal mode. At this stage, be very careful because you will have full privileges on the system.

3-  type:   fsck -fy  then press enter. fsck command will check/repair your hard-drive.

4- type:    mount -uw /  then press enter

5 –  type:   chmod 775 /  then press enter

6 – type:    reboot   then press enter. The mac will reboot and the glitch is gone…(hopefully)