Hi, my friend is having a big issue with his Imac after installing the most recent updates. He installed the updates and then the computer never restarted as it said it would. Then applications began quitting unexpectedly, and then he restarted his computer. Then when the computer booted up, the screen was gray with a message in the middle of the screen. The message says that you need to restart the computer by holding down the power button. He did, and the same message popped up. Behind the message it says, "panic(cpu 0 caller) Unable to find driver for this platform: "ACPI"
Debugger called: <panic>
Kernal Version: Darwin Kernal Version 8.4.1. Tuesday January 3rd.

you need a bootable CD

see this for troubleshooting OS X boot/install

see the Apple Support Article

Nothing happens when a disk is put into the computer, and the wireless mouse and keyboard also do not work when the message appears..

You have to hold down "C" to boot from a cd. The kb should work for holding that down unless something serious is wrong with the hardware.

Thank you for your very helpful repsonse..it worked!