Roberto,

It may be that you might have corrupted Tiger disk...
Try this - get the system disk that you wish to install tiger on. Install it into another Mac. Erase the hard disk, and install Tiger as usual. Repair disk preferences. Update to 10.4.6.
Reboot.
Shutdown and remove the drive. Install it in your 2.7Ghz.

It is always worth having a Firewire disk with two bootable partitions on it: one for 10.3.x systems with a ready to go OS version with everything setup, and one with 10.4.6 on it.
Here's how it works:
Boot from your firewire disk, by powering up the recalcicrant Mac whilst holding the Option key. Select the appropriate disk partition on your firewire disk. Use disk utility to erase the dodgy system disk.

You can then use Carbon copy cloner or Super Duper
http://www.bombich.com/software/ccc.html
http://www.shirt-pocket.com/SuperDuper/
to copy your disk partition onto the system disk.
Change the Start up disk in system preferences and off you go.

It is always worth repairing your disk permissions before doing a OS Update. Disk permissions can get messed around by dodgy applications, installers and drivers. Boot from your Mac OS disks and use Disk Utility to sort them out.

Hugh