Troubleshooting: PC doesn't turn on (no response from power button)

These are the steps you should take when a PC does not boot at all when attempting to fix and diagnose the issue.

NOTE: For each step that requires working inside your computer, you should turn your power supply off until you're finished working, then turn it back on when you go to test.

1. Ensure that the PC is firmly plugged in and that the power supply's switch is set to on.
2. If your computer power supply has a 115/230v switch on the back ensure that the voltage is set to the appropriate voltage for your country
3. Open your computer if it wasn't already and check over the 24 pin ATX cable and 8 pin ATX12v (may be a 4 pin on some motherboards) and ensure both are plugged in firmly.
4. Ensure that the RAM is fully seated
5. Ensure that the standoffs are correctly installed and there are no extra standoffs under the motherboard that do not correlate with screw holes on the motherboard.
6. Verify that the front panel header for the power switch is properly connected to the motherboard
7. Unplug the hard drive and disk drives and remove the video card completly. attempt to boot again, if boot up is successful reconnect parts one at a time to determine the problem part. If the problem part is the video card the issue might be power supply related or video card related.
8. Test to ensure that the power supply functions at all. The Paperclip Test is the most common method to do this. Click the link for directions to do the test. If the test fails the issue is the power supply

If any part except the video card in test #7 causes failure you can assume it to be the issue. If the video card is the issue in test #7 is the issue ensure that your power supply has enough wattage and 12v amps to handle the video card. If the PSU has adequate wattage and amperage then the issue is probably the video card, but could still theoretically be the PSU being unable to deliver it's full power due to a defect. Cross reference parts to a different PC if possible otherwise assume the video card first

If the PC fails to boot after checking all of these and the PSU is determined to be functional, it is reasonably safe to assume the issue is the motherboard.