When I'm cold booting from my computer, this happens:
Motherboard Logo > Windows 8 loading logo > Black screen.
In the black screen, keyboard "num lock" key does not toggle the num lock LED. Pressing the power button once on my PC tower and wait a few minutes, my computer didn't shut down (it would if Windows is loaded properly but simply not displaying). The only solution is to force shut down by holding the power button for 5 seconds.
And then I'd power it on again, but this time (perhaps because the PC isn't cold in temperature??), it would work normally:
Motherboard Logo > Windows Logo > Login Screen > Desktop.
Now, in the desktop, everything is fine. Then:
If I click "restart", it will restart properly, and everything will be fine.
If I click "shut down":
If after it shuts down, I power it on immediately, everything is fine.
If I wait about 10 minutes (perhaps because the PC is cooled in temperature??), situation goes back to the beginning of this post.
I have tried to update GPU driver, uninstall GPU driver, change cable (from Display Port to VGA), unplug all USB devices except my mouse, disk scan, nothing changes.
My PC spec:
i7-4790K @ 4.0GHz, 2x4GB ddr3 RAM, 500 GB SSD, GTX 970 GPU, Gigabyte Z97X Mobo.
I'm out of ideas now... any help would be appreciated!