Ok so this is my fist post and visit to the Tech Forums (Hiya!)
Have you tried swapping your ram sticks? The rig I built just four days ago Worked for a day then it stopped turning on in a similar way to yours. In the middle of troubleshooting I removed one of my two sticks and it booted fine, I put the other stick back in to make sure of the ram problem and it stopped booting.
Great Day and good luck!
cronus97