Weird Boot Up Issue

Hello All This morning when I turned on my computer it did the following, cooling fans, CPU fan, HD light they all come on for 3 seconds then go off for 2 seconds this process repeated itself for 10 mins before I gave up. I have tried the following, put in a known good power supply from another computer, tried a different hard drive, changed the on off switch, unplugged both dvd drives. Still with no change. This is a computer that I built myself a little over 2 years ago. It has an Intel mother board DH55HC with a Intel core I3 processor, a western digital black 500 GB hard drive. Up until this Morning I have had no issues what so ever. Any suggestions would greatly appreciated. Thanks Ray

Well you have certainly tested the extremes lol, given your post the only thing I could suggest is to reseat the heatsink, it's not uncommon for the thermal compound to become less effective than it needs to be to protect the CPU from heat damage, and the system refusing to start is a symptom of this, so do this and see if it helps. One main thing to note, clean off the old thermal compound before adding any fresh material, failure to do this will result in contamination of the new compound, and reduce it's effectiveness, and don't forget to clean both halves (the CPU and the heatsink) before applying the new material, hope this helps.