Answer to "No startup after CPU and SSD replacement, diagnostic LED confusion"This is a good lesson for those who believe they can “save a few bucks,” as I did repeatedly when I was young and had more initiative than brains.. I was proud of not being a quitter, but really I was just slow learner at times. Stubbornness = ignorance and pride. That lil’ combo is downright dangerous. Many times it actually costs you much more than if you spent the money upfront the first time and just bought the best. I learned this from buying basses. I bought 4 or 5 basses that were ok, but every one ended up having some issue. I knew I should just buy a Fender P bass and get it over with, but no. I bought a Gibson EB3 instead. The night before our biggest gig to date, it shorted and squealed in the middle of a song. l lifted it over my head and in the way of the “Who,” slammed it on the concrete floor breaking the neck into 3 pieces. The band looked at me, and said, “so whatcha gonna do now,” laughing at me. The next morning I went to the music store and bought that P bass. That was 1973. I paid $325...
Answer to "LCD Backlight not working"Which OS are you running? Many newer OS’s such as Mojave on your unsupported iMac will disable the backlight. If that’s the case check out macforums.com unsupported Mojave thread for the fix. They have a link to the fix.
Answer to "My iMac will not not boot from or to ANYTHING"Have you reset SMC and PRAM? This model has a known defective GPU also. @dan ‘s request to attach an external monitor will tell you if this is the culprit. Inside the iMac there are 4 diagnostic LEDs. Before you go that far start it in safe mode and see what the verbose readout is. It may give you your needed information.