Things to do/try, not really in any particular order.
1. Did your PC turn on okay before, or is this a new build?
2. Is the standby power LED on the motherboard lit?
3. Be sure the modular cables on the PSU end are fully plugged in, and the 24-pin connector on the motherboard too..Check for bent/damaged pins/terminals.
4. Disconnect the PWRSW (Power Switch) connector from the motherboard
front panel header (refer to your motherboard manual, if necessary) and momentarily jumper the two with a screwdriver, paper clip or something metal, and see if your PC turns on, as it should.
5. Get an el cheapo digital voltmeter from somewhere (auto parts store, or wherever) and check all the voltages and grounds on the
24-pin motherboard connector from the PSU..The image in the link is as you are looking into the connector end..You'll need to turn the unit on with the EVGA Tester Tool or jumper the PS_ON terminal to a ground with a wire or paperclip..Or take it to a PC repair place and have it tested.
6. Try another PSU, and use the cables from the other PSU.
See also: Advanced voltage testing in the
How do I test my power supply? EVGA FAQs.