My G5 iMac developed problems after upgrading latest updates to Tiger, iTunes, QuickTime, ect. I am now unable to access apps like system preferences, iPhoto, Safari and others. Also it will sleep but unable to shut down. I'm hopeful a new install of my OS 10.4 disk will correct things but fearful my photos, music and FireFox bookmarks may be lost. Any ideas? Asking for help to protect me from my own ignorant self. My beloved G5 has been flawless till now.