Erratic startup behavior. Power On, Power Off, and second Power On needed for boot


I've recently built a new desktop computer, and I'm having really weird startup issues. Basically, after the computer sits around powered off for several hours, when I hit the power button, the system powers up but does not display anything to my monitor, does not power up any peripheral devices (like light up my backlit keyboard), and does not trigger any hard drive activity. It just sits there without effect, but the fans spin and the drives are powered.

However, if I hit the power button to turn off the system and then hit the power button again within a few seconds, the system starts up correctly. In this case, the BIOS flashes, peripherals power up, Windows boots, and everything seems fine.

At this point, I've taken some different actions to try to isolate the problem:
I've reflashed the BIOS with the latest version
I replaced the motherboard battery
I replaced the power supply
I have taken the system apart and put it back together again, checking cables, RAM, CPU, etc.
I've cleared and reset the BIOS and double-checked the RAM timing and voltage.

I'm a bit stumped at this point. Does anyone have any other ideas? Should I contact Gigabyte for a replacement board? Is it possible that my case itself might be causing compatibility issues with the motherboard?

My specs are as follows:
Gigabyte AG-z77X-UP5 TH
Core i7 3770k
Corsair 650 Watt Modular
Radeon Sapphire 5770
2 x 2gb G.Skill Ripjaw DDR3 1600
2 x 4gb G.Skill Ripjaw DDR3 1600
64gb Kingston SSD
Seagate Barracuda 7200.12 ST31000528AS 1TB
Thermaltake Element G VL10001W2Z Black Steel / Plastic ATX Mid Tower Computer Case

Any help or suggestions would be greatly appreciated!!!


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More about erratic startup behavior power power power needed boot
  1. Remove/check/swap the fans connected to the motherboard, especially the one on the CPU fan header, I've seen a similar issue where the fan wouldn't register as rotating fast enough on the first "boot" but if the button was pressed again it would work (this was confirmed by manually spinning the cpu fan and it would boot first time).

    It is a strange solution, but it at least gives you something else to look into.

    Alternatively, and probably more likely, the PSU might also be on the way out and fails to provide the right voltages when first turned on until it warms up a little. Easiest way to find out if this is the case is to swap it out with another PSU.
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