Hi daddyof1,
Welcome to the HP Forums!
I understand that your desktop is experiencing some display issues, and I would be happy to be of assistance!
To begin, I will need to know what the Product and Model Number of your computer.
In terms of the desktop / tower, please follow this document on Troubleshooting Power Supply Issues. This should help in identifying any possible hardware issues.
The second step will be to diagnose the monitor. To do this, please refer to this resource on No Signal then monitor going to sleep shows on the screen. This should help in bringing your desktop out of a sleep mode state.
Please re-post with the results of your troubleshooting, and I look forward to your reply!
Cheers