Here is a strange one,
I needed to replace a dead hard drive in an imac g5 20. I put in a 500gb Western Digital sata drive and was able to boot from 10.5.4 retail disk that i cloned onto a firewire drive.
I was able to format and install the os. When went to restart the machine, it could not find the drive. When I booted from the firewire drive I was able to see the start up drive.
I dug up the original 10.3 discs and follow the same process, I reformatted the disc and did a clean install of operating system
When I restarted, It did not see the drive.
I thought this was a problem with the sensor, so I ran Apple Hardware Test and Tech Tool Pro and did not find anything wrong with the memory, logic board or drive.
I have reset the PMU, reseat the ram, without any progress.
I have never seen this behavior before, I would appreciated any feedback.