Cpu Failure to start up

Hello, okay so not to long ago i shut my computer down and it didnt shut down all the way, however the green power light turned off, and a red HDD light remained on... so i shut it down the rest of the way in the morning ( when i noticed ) and tried to turn it back on.. all i got was no power LED and a solid red HDD led and my monitor doesnt show signs of life but it works, however my fans and HDD spin, my keyboard blinks the num/cap/scroll lock once, and my mouse shows steady life. so i began to do the basics, swap ram out 1 by 1 and even added a stick i know that works, still no change, so, i swaped HDD themself, and still no change, i swaped GFX card, yet again, no change, i swaped my power supply, processor, CD rom, network card, C-MOSS battery, and still didnt get a change, so i swaped my motherboard and didnt get a change, ive tried every combo i can possibly think of.. once i swaped cases i got a somewhat different responce, wich is a green power light, and a very quick flash of a hdd light, but still same basic results, can anyone give me a clue or a solid answer? thanks!