|trvlr, Decades ago (when I knew everything), I would have considered it silly to think about the power cord, but I am sadder and wiser now. Several years ago, I replaced a power supply in an old computer only to discover that the power cord was defective. After reading your comment, I rushed to try it while miffed at myself for not thinking about it sooner. Unfortunately, neither the power cord nor disconnecting power to the hard drives changed the problem. The on time and the off time is approximately the same. I measured them as "Thousand 1, Thousand 2, Thousand 3, Thousa". My guess is that the on time and the off time are around 3.5 +/- 0.5 seconds each. Disconnecting the 12 volt 4 pin ATX connector enables the fans and lights to run continuously.|
Another comment I saw in a related thread was to remove the motherboard, look for shorts, and clean any dust off of it. I did try to remove the motherboard, but I could only get as far as removing the screws that hold it into the chassis. The back panel connectors and ports (keyboard, mouse, USB, RJ-45, audio, etc.) Seemed to lock the motherboard to the rear of the chassis. I was not happy to remove the motherboard anyway, so I put the screws back in. I did look closely at the components, but I do not see any that appear to be damaged. My next step will be to get a can of compressed "air" and blow the accumulated dust off the motherboard and out of the computer.