I have a 2011 27 inch iMac. I noticed that it was making a regular clicking/ticking noise (like a clock) when switched off. After ignoring it for a couple of days (during which time I turned the computer off and on two or three times) I decided to investigate. I unplugged the power cord and the noise stopped, but now that I've plugged it back in the computer won't turn on. It's completely dead. Research makes me think the PSU had developed a fault and has now failed completely. I intend to buy a replacement and fit it myself (I've had the iMac open in the past to install an SSD) but before I do this I thought I'd see if people agree that PSU is the likely culprit and if anyone had any advice or recommendations for me. Thanks in advance.