try plugging it in to a different power point
check all the connections are securely plugged in and one has not come loose
reset the cmos
does the small light on the m/b glow
check it is not a faulty case button by touching the 2 pins the case button connects to on the m/b with a small screwdriver for a fraction of a second and see if it boots
reseat the ram
check all the connections are securely plugged in and one has not come loose
reset the cmos
does the small light on the m/b glow
check it is not a faulty case button by touching the 2 pins the case button connects to on the m/b with a small screwdriver for a fraction of a second and see if it boots
reseat the ram