Hello I have a real weird problem, I've updated my Tiger 10.4.11 to Leopard 10.5.1 and now in an neverending reboot loop. My MacBook (2Ghz Core Duo, 2 GB Ram) starts, then I get a grey screen with Apple Logo, then after 2 minutes, the computer reboots and so one.... To stop this (infinite) reboot loop I need to put the Leopard DVD !!!! in the drive and wait for an unknown time of reboots to finally get the login screen. After that I can log in and use Leopard without any problem. I have no clue, what is going wrong, I've checked the Startupitems ( none, deactivated the Time Machine) and reset PRAM several times... I'm really upset because I really don't know why the MacBook is rebooting and needs the Leopard DVD to correctly boot ??? Thanks a lot for your help !