You are installing an additional drive into a working computer. The computer won't power up at all, no lights, no spinning drives, nothing.What's most likely the problem?

There must be problem with cordthats why the computer won't power up.

The power cord may not be rightly plugged

Check the power cable , if is connected and well than power supply of PC which the main supply for the power to PC 

There must power cord problem

check if it's not an alimentation problem . if it's okay then check the Bios

Could be power outlet, power cord or maybe loose cable connection.

i think the problem maybe in the alimentation

check the power supply or the plug and cord.

Possible answer to that question is that your power supply that provides sufficient DC wattage is totally dead.