Weird Case, PC turns on and off by itself for 1 second each. No beep No post

I was playing when brownout sudden occured and so while waiting I've decided to clean my PC and the lights were back up just in time i was about to finish putting the components back together. The PC turned on for about 10 mins and suddenly it turned off without warning. I tried to turning it on again but no response.. That time i found the main problem after slowly removing components and turning it on which is when i plug in the 4pin atx to my H61MXV Foxconn motherboard the system wont power on but as i unplug it the system runs for a split second and so I decided to buy a new Motherboard which is Biostar H61MGV3 ver7.5 and now arises a new problem. THE SYSTEM WILL TURN ON AND OFF BY ITSELF FOR A SECOND EACH REPEATEDLY. NO BEEPS. What i reused is my intel i3 2120, and 1 stick of Emmax 1333Mhz 1.5v 4GB and Corsair AX 760. Ive tried clearing CMOS, using another brand of ram which is Strontium 1333Mhz 1.5v, Ive also replaced my heatsink with a heatpipe and reapplying thermal paste, Ive also tried cleaning the RAM and CPU with an eraser, Ive tried to run the system without the case, I've tried replacing the CMOS battery, I also tried running manually my psu and using it on another pc and its ok . I also tried turning it on with just the cpu, the 4pin and the 24pin atx and I've tried to magnify the mobo cpu socket for bent pin but there was none and at the end of it IT WAS STILL THE SAME.. even if i try turning it on with or without my video card Palit GTS 450 and so what I suspected is a DOA mobo and i have it replaced with lga1155 Gigabyte GA-B75N ITX. and guess what, THE PROBLEM PERSISTS and the mobo i sent back which is Biostar H61MGV3 ver7.5 is actually working as what they informed me.. pls help me

What i never tried is replacing the cpu (because I dont have another LGA 1155 processor) or any of the people here in my place has the LGA 1155 socket mobo to try. I also never tried replacing the ram according the memory support list of Gigabyte GA-B75N ITX in 1333Mhz. The reason I can't think its the ram incompatibility because my first mobo the h61mxv doesnt list the emmax and strontium as supported brand but it was working with it and how come it wouldnt be compatible with much late mobo Gigabyte GA-B75N ITX.