If its automatically powering down, this is likely a hardware problem. I would do this:
1) disconnect ALL hard drives and boot, trying to get into bios. If that works, you know your system is okay.
2) Now connect ONE hard drive, the one you want to boot from. Make sure its data and power connectors are both fully seated. Then boot into bios once again and check to see if the hard drive appears there. If so, you know your hard drive is at least working.
3) Now boot into windows. If it does not work, post back with details of what happens.
My Computer
At a glance
Win7 pro x64stock i7 7700kCorsair Vengeance LPX 16GB (2x8GB) DDR4 @ 320...integrated Intel HD 630
Computer type
PC/Desktop
Computer Manufacturer/Model Number
diy
OS
Win7 pro x64
CPU
stock i7 7700k
Motherboard
Gigabyte Z270N-WIFI mini-ITX
Memory
Corsair Vengeance LPX 16GB (2x8GB) DDR4 @ 3200MHz
Graphics Card(s)
integrated Intel HD 630
Sound Card
onboard Realtek ALC1220
Monitor(s) Displays
two vertically mounted samsung 55" 4k un55mu8000
Screen Resolution
1920x1280
Hard Drives
256GB Samsung EVO 960 M.2 pci-e NVMe SSD
PSU
SilverStone Nightjar ST45NF 450Watt Fanless
Case
No case. Motherboard is mounted directly onto power supply
Cooling
Evercool low profile 815EP with Panaflow 12L fan at 7v
Hi guys. All is well again. I pushed the start button & it repeated the fail to start story. I walked away in disgust. Returned after a time to try again. Merely tapped the start button (not pushed) & it responded by starting as normal.
I haven't shut it down since. I don't want any bad news. So an odd glitch that seems to have fixed itself. I'll return if it continues. Sorry to bother you. Thanks for responding.
My Computer
At a glance
Microsoft Windows 7 HomePremium 64-bit 7601 M...Intel(R) Core(TM)2 Duo CPU E4500 @ 2.20GHz8GbNVIDIA GeForce GT 710
Computer type
PC/Desktop
Computer Manufacturer/Model Number
Generic - custom build
OS
Microsoft Windows 7 HomePremium 64-bit 7601 Multiprocessor Free Service Pack 1
CPU
Intel(R) Core(TM)2 Duo CPU E4500 @ 2.20GHz
Motherboard
Gigabyte Technology Co., Ltd. EP35-DS3P
Memory
8Gb
Graphics Card(s)
NVIDIA GeForce GT 710
Sound Card
(1) USB Audio Device (2) USB Audio Device (3) NVIDIA Hig
Monitor(s) Displays
older 21" thinkvision brand?
Screen Resolution
1680 x 1050
Hard Drives
WDC WD5000AAKS-22A7B0 ATA Device
ST3500418AS ATA Device
ST3320813AS ATA Device
Hi guys. All is well again. I pushed the start button & it repeated the fail to start story. I walked away in disgust. Returned after a time to try again. Merely tapped the start button (not pushed) & it responded by starting as normal. I haven't shut it down since. I don't want any bad news. So an odd glitch that seems to have fixed itself. I'll return if it continues. Sorry to bother you. Thanks for responding.
The start button itself is a momentary switch that creates a brief closed circuit which signals the motherboard to start. When you had that undesired power-down after 7-8 seconds what likely happened was the switch got stuck in the closed position for too long. If it happens again you can spray some silicon lube around and inside it, or replace the switch itself for $2-$3.
My Computer
At a glance
Win7 pro x64stock i7 7700kCorsair Vengeance LPX 16GB (2x8GB) DDR4 @ 320...integrated Intel HD 630
Computer type
PC/Desktop
Computer Manufacturer/Model Number
diy
OS
Win7 pro x64
CPU
stock i7 7700k
Motherboard
Gigabyte Z270N-WIFI mini-ITX
Memory
Corsair Vengeance LPX 16GB (2x8GB) DDR4 @ 3200MHz
Graphics Card(s)
integrated Intel HD 630
Sound Card
onboard Realtek ALC1220
Monitor(s) Displays
two vertically mounted samsung 55" 4k un55mu8000
Screen Resolution
1920x1280
Hard Drives
256GB Samsung EVO 960 M.2 pci-e NVMe SSD
PSU
SilverStone Nightjar ST45NF 450Watt Fanless
Case
No case. Motherboard is mounted directly onto power supply
Cooling
Evercool low profile 815EP with Panaflow 12L fan at 7v
