possible motherboard failure.
Try removing all RAM (memory) sticks from the machine when the machine is off. Try powering on the machine with no memory your machine should beep load and clear it has no useable memory i think the code is 1-3-3-1 (1 beep, 3 short, 3 short, 1 beep)
Any beeps a good note down what beep you get - check here for beep codes:http://www.computerhope.com/beep.htm
no beeps = Not good possible motherboard or cpu