Dell Precision 380 not starting . Stable orange light.

My.pc is not starting and showing a stable orange light instead of green. When i switched on the fan rotate at a high speed and showing a orange light. I have tried all the options by searching on internet o refreshed the pc by pressing power button by removing and inserting coing and every method that is possible i have tried i have also changed PSU but my PSU is ok. I am not sure about mobo that ispk or not . tell me what i do to check mobo. Or if mobo is faulty then how to solve this issue.