It's either the new PSU gone dead, or the motherboard failing because of damage done a week ago. What does your repair man say about it? He can measure the output of the PSU or try another.
English is not my first language, pleace bear with me. My mother accidentally unplugged my power strip, that cause the pc shut down violently, but she immediately plugged back in. After that, my computer was intermittent boot. Then, I tried diagnostic, and the repair man said my psu is already dead. Therefore, I request a new replacement from Evga since my psu still has warrantly. The first week was totally fine after I received the new psu, but now my computer is dead again. It show no sign of power except the led light of my keyboard. However, I can still forced my keyboard led light to went off by holding down the power button.
Cpu: i5 2400
Mb: asrock z75 pro3
Gpu: r9 280x
Ram: g.skill ddr3 2400