I have a EMACHINE that was downloading norton updates ( may not be related to the issue ) and then shut down. Now there is no power. Changed the power supply and power cord, the led on the mother board comes on but still when hitting the power button I get nothing. Checked all the connections and they are good. Im thinking the cmos battery or the motherboard. Is the cmos even a possiblity or could it be the power button connections WRONG. But Im not sure.If you have two RAM sticks, try booting with just one at a time. Try booting without any RAM and also with the hard disk (and any other drives) disconnected. Take the front cover off your PC - this should EXPOSE the power button, make sure it is clicking correctly when you SWITCH the PC on. If you have a spare PC, try using your RAM in that to test it. Also try connecting your hard disk as a slave.
You have ALREADY ruled out a faulty PSU, if you can also rule out faulty RAM and HDD, it will be either the CPU or motherboard that is at fault.I ran into the same error before. Okay try takeing out the RAM if you get a beep from the MotherBoard its Okay if not it probably got fried. Then try one RAM stick at a time if you see anything one of them is bad, if nothing shows up your CPU is dead and should be handled with care when you put in a new one. Hope that helps.