I am from Dell Social Media and Community.
I am sorry to know that you are facing an issue with the system.
If your system has power and is not booting up there could be several possibilities for this issue.
Before we proceed to the troubleshooting, I would like to know:
Do you have any lights on the power button?
Does any of the lights blink on the computer? including the power button?
Does the system make any beep sounds?
What is the system model number and how old is the system?