Try the steps below. There's a note about a failing firmware update, you may be able to create a Firmware recovery CD. Full article is here: http://support.apple.com/kb/HT1557
"Hold down the power button until the power indicator light flashes, then release it. A long tone will be heard, then a gray screen with an Apple logo appears. There is a progress bar under the logo. As the progress bar moves, your firmware is being updated.
Important: Do not unplug, shutdown, or restart your computer while the update is taking place. Interrupting a firmware update can render your computer unusable. If this happens, take your machine to an Apple store or authorized service provider or perform the recovery yourself using another Macintosh computer to download the Firmware Restoration CD disk image from http://www.apple.com/support/downloads/. This software allows you to create a CD which you can use to restore your machine to working order.
At last taken out the CD manually, when I switch on Macmini inserted the Firmware Restoration CD, only light glows nothing happens, Pressed button C to boot with CD & I tried the steps provided below but no luck
Turn on the computer and continue holding the Power button. The sleep LED will blink rapidly, then slowly, then rapidly (3 quick blinks, 3 slow blinks, 3 quick blinks).
On Macs that don't have a sleep LED, tones are used instead. Hold down the power button until you hear 3 long tones, then 3 short tones, then 3 long tones.
On Macs that use a tray-load optical drive, the tray will open to allow the Restoration CD to be inserted.
Insert the Firmware Restoration CD while the lights are blinking or tones sounding, then release the Power button. A long tone is played once the recovery process has started.
A progress bar appears beneath an Apple logo on a gray screen. The progress bar indicates the firmware is being updated. Do not disconnect power, shut down, or restart the computer during the update or you will need to start the restoration process again beginning with step 6.
(suspecting that chip may got failure due to power off whlie updating firmware or any hardware problem?) need help.