Three days ago I bought parts for a new computer and built it. This morning I went to turn on my computer and it would just power cycle. It would turn on for about a half second then turn right back off. A few seconds later, it would do the same thing and this keeps going on until I pull the plug from the power supply. At first I thought it was a defective power supply so I went out and bought a new one. After connecting the new hard drive, the same thing happened.
I then unplugged EVERYTHING from the motherboard except the processor and the cooler for the processor. I try to turn it on and the same thing happens. I have an ASUS P8Z68 Pro/GEN3 with an i5-2500k and a Cooler Master 212 Hyper Plus.
Does this sound like a defective motherboard or a bad processor?
I have seen this before, I also use ASUS motherboards.
The PC would power up for about 1 second and then power down. I replaced the power supply but it didnt solve the problem.
The problem was that one of the screws holding the motherboard in place.
The screw's head was a millimeter too wide and reached outside of the area marked on the motherboard.
Ensure that you use the correct screw for the holes that holds the motherboard in the box.
Also make sure that all power slots on your motherboard are plugged in. It is easy to miss one of those smaller power plugs (the one with 4 wires).
I have only ever encountered this problem with ASUS motherboards, normally there is more than enough space around the whole for larger screws. I would recommend to only use the screws that ASUS provides specifically for that purpose.