Desktop Not Working Properly

Hello,
When I start my pc,its starts fine sometime.after sometime it automatically stop working.sometimessmps fan also get stopped or sometimes it works fine.I replace my old smps with new one but i found same with that also.when i found that system is stopped then i found that the green light is glowing in front of CPU & also in mother board.But no red light or display is there.Is it mother board related problem or power supply problem i cant able to realize and no one cant able to tell me.so its very helpful that if anyone plz help me out of that problem..

Thanks

Subham