PC Won't Turn On — Zero Power Diagnosis

Check the basics

• Is the PSU switch on the back set to the I (on) position?
• Try a different wall outlet and confirm the power strip is on.
• Is the power cable fully seated at both ends?

Isolate to PSU or motherboard

Perform the paperclip test on the 24-pin connector (bridge green to black). If the PSU fan spins, the PSU is delivering power and the issue is on the board. If the PSU fan does not spin, replace the PSU.

Short the power header pins

The front-panel power button cable may have failed. Use a flathead screwdriver to briefly bridge the two PWR_SW header pins on the motherboard directly. If the PC starts, replace the front-panel cable or button assembly.

Clear CMOS

Remove the CMOS coin battery, wait 30 seconds, reinstall. A corrupt BIOS setting can prevent POST from even beginning.

CPU power

Confirm the 4-pin or 8-pin CPU power connector near the top of the motherboard is fully seated. A loose CPU power connection causes no-power or no-POST symptoms.