Hey guys. I'm having problems upgrading my Mac G5 from osx 10.4.11 to 10.5, any help would be much appreciated! Cheers

Hey Guys. I recently bought a Mac G5 from a friend as a tool for music production (which it has been great for) but I recently thought I would upgrade the OS to osx 10.5 (it was previously running on osx 10.4.11). However, the installation does not appear to have been successful. When I turn the mac on I get an option to select the language, and once that is done it goes to the osx 10.5 installation screen, and thats where it stops (as far as I can tell). It won't let me do anything, even cancel the installation. If there is a way I can either cancel it or complete it successfully (with all my files still there) then I will do so, but I am currently at a loss. If anyone could help I would really appreciate it! Cheers