If you had a Blackout/Brownout power outage and you don't have a Surge Suppressor installed to protect your computer, when power was restored it probably sent a high voltage spike to your computer. Possibly burning out your Motherboard and could have also damage any hardware connected to the motherboard or it most likely damaged your PSU.
You can check your PSU power outputs with a Multi-meter to see if you are getting the proper 12.0/5.0/ 3.3 Vdc.
You can disconnect all cables to the Motherboard and use the main 24 pin Motherboard connector to enable the PSU to turn on by shorting out two Pins on the 24 pin Motherboard cable with a paper clip.
If the PSU checks good then most likely your motherboard got fried by the High Voltage Spike. The PSU offers some protection but it isn't a Surge Suppressor.