Hi everybody I'm seeking response to a rather strange problem. Around January (2014) I bought a used 2011 21.5 iMac (2400S, HD6750M) and soon installed a Samsung 840 EVO 120 GB SSD and additional 16 Gigs of RAM for a total of 20 Gigs (pre-installed 4 Gigs). Everything was doing just fine, until one morning when the iMac wouldn't boot. I took it to an Apple-certified repair/reseller (Eplehuset). They took a look at it and said that I had to change the logic board. After some thought, I bought a new logic board on eBay along with a new video card module (it too was a HD6750M). I installed the parts, and everything was running just fine until recently, when it wouldn't boot - again. Some of the circumstances are similar/the same: - I'd just been running Mac OS X (DIY Fusion Drive; SSD + 250 Gigs of HDD) and had selected the Windows partition (the remaining 250 Gigs of the HDD) for start disk. - The computer chimes - The panel lights up (i can se the lights turn on) - Image remains black In both cases, I've tried all the SMC, PRAM/NVRAM, etc. - no dice. However, this time around, I can see some heat markings on the logic board itself. It wasn't like that, the last time. I've attached some images, so you can compare for yourself: These two shots, are images of the old logic board. It did occur to me, however, that my installation of the SSD might have changed/obstructed the internal airflow. As you'd might now, the heatsink for the video card is in the top of the case. What bothers me is, that I've been gaming for hours (in Mac OS X [Portal 2, CoD4:MW] and Windows [SupCom:FA and other games]) without any problems. I switch between Windows and Mac OS X on a daily basis, so please don't consider this as being Windows-bashing. It's just my observation, that both times, I came right from Mac OS X, chose Boot Camp as start disk, hit reboot, and bam! Dead iMac. Any thoughts? EDIT: Oh. Forgot to mention, that in both cases, the diagnostics LED's on the logic board, shows no sign of trouble (all four lights up just fine).