@Donnabd Welcome to HP Community!
I understand that all in one will not start.
Please attempt the below steps:
Attempt a BIOS recovery > All in one
If the above steps work and the display turns on: Perform a hardware test to be on a safer side.
If the steps didn't work, use the below links for further assistance:
Computer Starts but Monitor/Screen Remains Blank : Click here
HP and Compaq All-in-One and HP Touch Smart Desktop PCs - Screen is Blank after Starting the Computer: Click here
Keep us posted,
If you would like to thank us for our efforts to help you,
Give us a virtual high-five by clicking the 'Thumbs Up' icon below, followed by clicking on the "Accept as solution" on this post,
Have a great day!