bought it from CL. I put a PATA HD in the optical slot so I would have all 4 SATA bays free for non-boot drives. I did not power the system on when I bought it nor before installing the HD. It made a crackle/pop sound and does not turn on at all. I tried resetting the SMC. No go. The seller said the system hung at the "We aint finding an OS" screen. Drive is not showing up in Yosemite. Shows up as a "protected partition" in XP. I could not format it WITH XP and did not try a 3rd party. Anyone have this happen? Is there anything to look for/at?