My name is Kaushal and I work for the Social Media and Community Team at Dell. It sounds as if the trouble lies with the video display of the system as it should display some lights on the monitor’s power button.
And, hence might have the power cable disconnected for it or there is no post scenario where all of the components inside the tower are not getting enough power and hence refusing to come on and stays on a standby state.
Waiting for the reply!!
Hope this helps!