You did not hear the beeps (or you heard a continuous tone).
Obviously that is bad. But we've narrowed down the failing item in your computer to either the motherboard or power supply.
Technically speaking, you also may have heard no beeps because your speaker is faulty, but the chances of that are so low that I am going to discount the possibility. However, now is a good time for you to check that you connected up the speaker correctly.
If the power supply fan is turning, that does not prove prove that the power supply is good. All that proves is that part of the power supply is good.
If you have a spare power supply, now is certainly a good time to try it.
Click here if the power supply fan is turning (continuously).
Click here if the power supply fan turned for a fraction of a second and then stopped.
Click here if the power supply fan is not turning.