Computer keeps turning on and off

[foji895]

I built a computer in 2011. Recently, I unassembled it to clean it. When I put it back and tried to boot it up it doesn't turn off. I turn on for 1-2 seconds and off and keeps doing this unless you unplug it. Once in a 20 tries, it turn on for 15-20 seconds and then turn off. Yesterday it turned on for 5 minutes and then off again. I changed the RAM, PSU but the problem is still there.

Motherboard- Gigabyte GA-z68x-ud3h-b3
intel i7-2700k

I don't have it in a case since its easier to troubleshoot that way.

 

[anotherdrew]

How aggressive was the cleaning? Vacuum cleaning hoses can build up static electricity which is not good for computer parts.

How much did you disassemble? This is the more likely issue that something didn't get plugged in all the way or get plugged in wrong is creating an intermittent short. A dropped screw that is sitting on in the wrong place is also possible.

When diagnosing these issues I try to start simple. Unplug anything you don't need (all RAM except 1, Video card, hard drives, etc). If it won't boot with just a MB, CPU, and 1 RAM stick, then you know the issue with one of those (probably MB, unless you removed the CPU and it's possibly not seated correctly).

 

[foji895]

I have changed everything (motherboard, RAM, CMOS, PSU). The computer has started up one time before so I know its no the CPU.

 

[anotherdrew]

New motherboard, new RAM, new PSU, old CPU ... that's all that is plugged in and it won't boot? Either you have very bad luck with new parts or something is up with that CPU.

You say you have the parts out of the case ... what are they sitting on?

 

[foji895]

I was look at the 20/24 pin PSU connectors and I noticed that one of the 20 pin slot is empty. It that normal? Yeah it is out of the case. It it sitting on top of a glass table and before that carpet. And I noticed that sometime when the keyboard is plugged in, sometimes it doesn't work.

 

[anotherdrew]

I would not work on carpet, not because of conductivity, but instead static electricity.

One pin on the 20/24 pin connector is optional. Sometimes it's there, sometimes not.

If its not starting with the keyboard plugged in (USB or PS2?) then that is an indicator that something is wrong there. BTW, most people don't know this, but PS2 devices should not be plugged in while the computer is on. At one time it was a pretty good way to fry your motherboard. Today most MBs will not be damaged, but it should still be avoided.