The topic of your post has been covered numerous times. The solution can be found by using the "forum search" to get what needs to be done. Review and try various fixes and/or attempts at one.
However, it usually always boils down to replacing the psu. Get a compatible one and basically get a bigger wattage unit. A brandname does better and spending money now will pay for itself.
FYI - provide system details to better help you.
My turned itself off and now won't turn back on again. If I press the case on-switch I do hear a slight click sound (I THINK it's from the PSU but can't be sure) and the ethernet card LED lights up at the back. Other than that, no life at all.
I'm guessing it needs a new power supply but could it be something else? I don't want to burn