U2515H "not detected by computer" "entering power saving mode"

Hi community

My Dell U2515H monitor details are:

serial number CN-0X48H6-64180-593-01UL
monitor attached to Windows 10 64 bit on Dell Latitude E6330 - out of warranty
Connection HDMI (monitor) to mini HDMI (computer)

GPU = Intel HD Graphics 4000; driver version 10.18.10.4425
OS = Windows 10 Pro (10.0.15063)

Powerplan balanced (recommended)
monitor resolution 2048x1152 (recommended) as reported in Display settings on Windows 10

The Dell Latitude E6330 computer has the following video out ports:

-mini-HDMI
-VGA serial

============ PROBLEM ===========
Since a few months ago the monitor is pretty much now permanently in power saving mode even when the computer is being actively used and effectively useless.

It says there is 'no signal coming from your computer"

It is not possible to wake up the monitor through mouse or keyboard activity.
The correct input source is selected on the OSD.
Other than being able to select the input source, I can't access any of the OSD menu as shown in the U2515H user guide.

I have powered off the monitor, disconnected all cables, waited 5 min and reconnected it. It worked once for a few hours until the next time i used the computer and didn't work again. repeating the steps didn't work again.

I have run full hardware diagnostics on the laptop and everything PASSED.

I have tried it with 2 other HDMI cables - same problem.

I have updated all drivers for:

Display adapter: Intel HD Graphics 4000
Monitors: Dell U2515H

- same problem.

the monitor works fine on another computer running Win 8 using a display port.

Please help.  it's a great monitor - when it works.  I suspect the problem is with Windows 10 but didn't get any help from Microsoft.