EFI ROM corruption on 2009
hear three long tones, three short tones, and then three long tones
Three long tones, three short tones, three long tones: EFI ROM corruption is detected, and the computer is in EFI ROM recovery mode.
Newer computers automatically recover from a corrupted ROM; when this occurs, a progress bar appears on the screen during ROM recovery mode. Don't disturb your Mac while the ROM recovery takes place. When recovery is complete, your Mac restarts.
If you need to restore the EFI ROM on certain Mac computers produced before 2008, you'll need to use a Firmware Restoration CD to restore the EFI ROM. Search Apple Downloads for the right CD image for your computer.
This is a 2009 and I get nothing on the screen. After doing a lot of research I find no definitive answers. Some have suggested changing the battery but I have never seen a battery failure on one of these.
After all these years I finally got in a genuine EFI failure (no Hanky Panky)
The battery was fine.
I ordered in a BIOS EFI firmware chip: Apple iMac 24" A1225 Logic board: 820-2491-A
from these guys on eBay
Put it in and it now works great! I was actually surprised ;-)
I emailed these guys and asked them to join us for some additional expertise.