Do you know what those updates were?

What color is power button on PC and steady or blinking?

Just because monitor is going to sleep doesn't mean it's working correctly. All that says is it's not detecting a  video signal. Can you test this monitor on different PC or different monitor on this PC?

Try clearing BIOS:

1. Power off, unplug
2. Press/hold power button for ~15 sec
3. Open case and remove motherboard battery (check Service Manual for details)
4. Press/hold power button for ~30 sec
5. Reinstall the battery (Time for fresh CR2032 3-volt coin cell battery? ~$2)
6. Close up and connect mouse, monitor and keyboard
7. Reboot

DID THE POWER OFF REMOVE BATTERY RESTART NOTHING

I DONT HAVE A LIGHT ON THE POWER BUTTON. THE LIGHT BLINKS ON THE CD/DVD DOOR

WHEN I DID YOUR REBOOT THING THE LIGHT ON THE POWER BUTTON WAS YELLOW BUT DARK NOW

MONITOR WORKS FINE WITH LAPTOP

Do you know what updates you did?

Go here and follow the instructions to do the BIST test on the power supply using the PSU button on rear of PC. What happens?

If you were doing a BIOS update that may have failed, go here and follow the instructions to start a BIOS Recovery.

GREEN LIGHT UNDER POWER CORD ALTERNATING ON AND OFF QFTER BIST TEST. ALSO TRIED BIOS RECOVERY WITH NO RESPONSE

Sounds like it may have failed the BIST test: "The light should be solid on not flickering or flashing"

Did you hear/see the PSU fan start spinning?

You may need to follow Resolve No Power, No POST, No Boot or No Video issues with your Dell Computer to see if you can identify the problem component.

WHEN THE LIGHT GOES OFF THE FAN GOES OFF.