So I thought I could get more years out of my 5 year old mid-2011 iMac by replacing the hard drive with a new SSD. I damaged something. LCD screen wouldn't light up. Shop said they had to replace the screen. Did that and it ran beautifully for 6 days, then started seeing the circle-slash gray screen, had corrupted drive. Took it to shop who ran diagnostic and said the hardware is fine. So I nuked the SSD and reinstalled the OS and my apps. Then bang, same problem only worse. My conclusion is that I wrecked something unhooking those four cables to the screen and created a cold connection gremlin. I doubt I'll find the thing and don't want to throw money at it. Fortunately I had an old 2010 white MacBook and good backups so I was up and running pretty quick, but slowly. Also fortunately it is a piece of cake to DIY that MB so I upgraded the RAM from 4 to 16 and replaced the hard drive with an SSD. In spite of being SATA II the thing really zips along nicely. I picked up a high res 27" monitor and the old MB drives it fine through Apple's expensive dual link minidisplay to DVI adapter. So all good while I figure out the next step. Probably one of the new iMacs this fall. I'd be happy with a Mac Mini but the rumours there aren't hopeful. Bottom line: I should have let the shop install that SSD. Thought my 25 years opening PCs meant I could crack the iMac. Nope.