Again try booting up with no extra cards or builtin features on (go into bios and disable onboard sound, graphics, nic, etc...) so you basically only have the video card and hard drive attached to the mother board when you boot. You may also want to download Memtest 3.1A and run it to test your RAM (RAM probably isn't the issue but another thing to try), also try a different power supply.

It may be that an onboard feature is defective, I had the builtin LAN go out on the kid's pc and it would crash until I disabled it so I just put in a cheap Intel NIC I had laying around and all is well.

i have did this all u write to me but did not solve problm.can u guide me in its
rapairing ( Mainboard D815EEA ). i can do evry soldring level work.

Well if your going for component level repair your in for a hard time unless you can spot some obvious leaky capacitors or open resisters on the board. A leaky capacitor will have some crud on the top of it usually so it will be easy to spot, I guess you could desolder it and find and exact replacement but there may be other issues as well and without a spec sheet on the board giving you reference points for voltage measurement and whatnot it would be hard to pinpoint a problem like that (been about 5 years since I had electronics classes in college so don't remember to much of that stuff). A bad cap or IC chip should look burned or broken so break out the flashlight and check out the board.
Unforetunately it would probably be easier to just replace that motherboard.