It sounds as if you either have a bad connection and/or PSU starting to fail. In any event it would likely be best if you are not familiar with such things, to take it to a shop and get it looked at.
my motherboard's green led light glows little and my computer does not start. when i just hit the motherboard two three times from outside then light glows more and computer starts. Computer also turned off automatically at any time and green light glows little. That means when green light glows more, computer runs ok and when glows little computer turned off or not started. What should i do. need some suggestion urgent.