Aright so I've re-read over your problems....if you're plugging in your video cable and it the light goes orange..that means you have a hardware problem....Did you ever once hear any sort of beeps when you go to power it on. The beeps are code that help you to troubleshoot which again you'd need the manual to cross reference what the beeps mean. Get memtest86+ and create a bootable CD or floppy and test your RAM to make sure that isn't crappy....if you have two sticks...try them seperately for errors...if they are clear...then try both at the same time..could be they just don't like each other....if you've tried two different graphics cards, it's probably not the graphics card and so it seems it's coming down to RAM, CPU, or Motherboard..and you said you were merely switching out motherboards...SOOOOo what COULD be happening is that when you seated your motherboard it's accidentally grounding out somewhere....you made sure to put in the metal studs before placing in the mobo right? So that it's not just resting on the metal? Grounding out of mobos is very common and will cause your Computer not to boot....Did you take your CPU off when you transferred the mobo to the new case? If not then I'd say the CPU probably isn't the problem....but when your computer doesn't boot, has no beeps, no signals to nothing, but you have power going to the system, then it's either the Mobo, CPU, RAM, or Video Card....since you've tested two different cards I'm going to assume it's not the card, if you didn't remove the CPU I'm going to guess it's not the CPU....so run that memtest and see if it's the RAM...if it's not the RAM then quite possibly the mobo is grounding out on the case.