I have a 2007 iMac (2.16 C2D) and after installing the new Tiger secrurity update my computer will not boot. It gets stuck on the Apple logo with the spinning wheel (not mouse). I tried safe mode, single user mode, and reseting the PRAM with no luck. I can boot from an external HDD that has Leopard installed and see the folders on the Mac HD. I backed up all my files. Does anyone know what's wrong? I guess I can reinstall Tiger but I do not have the install disk. Is there any way I can fix it without reinstalling Tiger, Leopard or any other OS?