So I got this iMac from auction, as is. The iMac chimes when I press the start button but the screen remains black. Is it possible that the iMac chimes if it has no CPU? I just wanna make sure if the iMac indeed has the CPU because I noticed missing screws on the front screen. I did not disassemble the logic board as I never done it. So is it possible to not have a CPU and still have the iMac play a chime when it boots up?
No, there will be no boot-up chime (an EFI ROM tone) if the CPU is missing. The chime only plays if the power-on self test completes successfully, which is impossible without a CPU.