[SOLVED] New Desktop - CPU light blinks once, fan doesn't start

Apr 14, 2019
Hi folks,

First time building a desktop here and I'm having trouble starting it off. I've read through the troubleshooting

And checked all the items except (since it's not even booting):
  • Did you install the system speaker
  • Is your CPU supported by the BIOS revision installed on your motherboard
  • Re-setting CMOS
  • Don't have a working PSU to test if it is at fault - will take machine to a repair shop later this week to see if they can test for me.
Here are more detailed symptoms:
  • Motherboard lights are on when I turn the PSU on
  • Once I hit the power button:
    • CPU led on motherboard blinks for 0.1s.
    • The CPU fan starts off only for 0.1s too.
Things tried so far:
  • Tested with 2, 1 RAM in different slots. Tested with 0 RAMs, always the CPU light that goes off
  • Moved Motherboard outside the case (anti-static mat)
  • Verified that CPU doesn't have any bent/damaged pins
  • Verified that the 24-pin ATX is connected to the PSU
  • Verified that the 8 ATX_12V_2X4 is connected to the PSU
  • Verified that the CPU fun is connected to the motherboard (CPU_FAN pins)

All brand new components purchased on Amazon
  • Motherboard: Gigabyte Z390 Gaming X
  • CPU: Intel i5 8400 LGA1151 (8th gen)
  • RAM: Aegis DDR4 16GB ((PC4 19200) Intel Z170/X99 Platform Desktop)
  • PSU: Seasonic, 650W, 80 Plus Gold
Any other ideas before I pay a visit to the repair shop and look into returning the motherboard / PSU / CPU?

Last edited:
Motherboard power connectors:
  • 1 x 24-pin ATX main power connector
  • 1 x 4-pin ATX 12V power connector
  • 1 x 8-pin ATX 12V power connector
The manual shows the 8-pin ATX power connector can possibly be connected using only 4-pins. It appears you didn't read the manual and didn't connect the 4-pin ATX 12v power connector.

you wrote:
  • Verified that the 24-pin ATX is connected to the PSU
  • Verified that the 8 ATX_12V_2X4 is connected to the PSU
Apr 22, 2019
Had this problem a while back, be very very careful. When I hooked up my old PSU my hard drive was cooked. Try with a different power supply, but unfortunately the damage is probably already done and the power supply was likely dead on arrival. Also that 8-pin you're holding is the CPU plug, should fit somewhere around the CPU fan plug. 4 pin connectors are for older CPUs, so if you have an 8-pin slot the 4-pin is unnecessary.
Apr 14, 2019
Thanks for following up. Your hunch is right, it was the PSU. I went to the repair shop and they tried with a different one and the system booted, so luckily no damage so far.
I just got a repl