Original post by: John B ,
Hi, I had the same problem on my iMac dual-core 3.06gHz. Stupidly I put in a firmware password and forgot it and I had recently blocked anybody accessing my CD drives etc. Even I was blocked. Therefore I couldn't wipe the hard drive and reload OSX. I got the blank white screen. This method got my iMac back. To do this you need to alter your RAM configuration first by adding or removing memory. This forces the PRAM to take action. You will still need enough RAM to run the machine of course. 1) After changing your RAM either up or down. 2) Using a wired keyboard, start computer with keys COMMAND-OPTION-P-R pressed in. You MUST use the COMMAND-OPTION keys on the RIGHT side of the keyboard. 3) Let the machine boot THREE times (mouse lights up on each boot cycle, turn it over to see) 4) After the THIRD or FOURTH boot cycle hold the OPTION key down ONLY. 5) A BOOT MENU should appear. I cannot remember if I hit EJECT on the boot menu or on the keyboard. Try each if it doesn't work first time. You can access your CD drive now, put in your BOOT CD (OSX disk). Reboot into Single User mode and reload your OSX system. At step (5) You may not have to reload your system files, just set up your PRAM.