I put together a custom built PC this week and had it working and booting up with no problems. However when I switched on my PSU yesterday, the motherboard would not power up and there were no lights on it and no fans/drives were spinning. Trying to solve the problem I unplugged the 24 pin ATX connector and plugged it back in to no avail. However after trying several more times the motherboard got power when the connector was half way in and when I pushed it fully in it still had power. The computer booted up and stayed on with no problems.. Until I switch off the PSU or unplug the mains lead from the socket - I then have to unplug the 24 pin connector and put it back in until it works. I think this rules out any faulty connections in the leads or motherboard as if the pins were bent then the motherboard wouldn't power and then not power after just turning off the PSU. And also I think it rules out that the motherboard or PSU are fried as they wouldn't start at all. This is a strange problem as the power stays on fine until removing power from the PSU. Does anybody have any ideas what is causing this problem?

My PC specs:
Gigabyte GA-Z68X-UD7-B3 (Motherboard)
Intel Core i7-2600K (CPU)
16GB Corsair Vengence (RAM)
EVGA GTX570HD Superclocked (GPU)
Corsair Professional Series HX850W (PSU)
2 x 1TB Western Digital Cavallier Black 7200rpm (Hard Drive)
LG BH10LS30 (Blu Ray Drive)
Edimax EW-7722In (PCI Wireless Adapter)
120mm Sharkoon Silent Eagle 2000 (Fan)
Bitfenix Colossus w/ 2 x 230mm fans (Case)

okay, lots of possible reasons for this error. ;)

1. Check that cpu and ram is seated properly, and see if you didn't accidentally have bend a pin in the cpu socket (can be very hard to see, but try to look anyway)
All the ram out and re-seat them.

Also check that all other connections to the motherboard (incl. PCI) is properly seated.

2. if that doesn't help, then try the PSU in another pc (if possible), or maybe try to use another PSU. -To isolate that as a factor.

Maybe try to boot with only one RAM stick, and try the sticks in different ram slots.

3. Try to boot using another graphics card. Maybe if you have an old one, or you can borrow one somewhere.

4. Still no luck? RMA the motherboard and the PSU together (if you bought it the same place). :)

The situation is similar to the follow case I have seen:

PC will not power on in the morning or after a period of time no use.
If reseat the power connectors on the mobo, and power on again, the PC boots and works ok. Or we tried just unplug the power cord and press the power button over 20 seconds to discharge the system, then plug the power cord back and PC powers on ok as well.

Once the PC powers on, it can be used for a full day without any problem.

Later on, the PC will not be powered on this way, no matter reseat PSU connector or discharge.
The faulty parts we found finally are both mobo and CPU.
Mobo chipset overheated and error codes were showing the CPU is not passing the sufficient voltag when initializing.

finally RMA the Mobo.

Hope this helps!
Bill
tech manager
WPTinc

It could be a short somewhere. It may be a bit of a pain to do this but try and take your MB out and put it back in again, could possibly work.