Still having problems,

There is no particular time, activity or sequence when the sleep/hibernate happens when I use the laptop.

:emotion-2:

First, I'd suggest you run 'Power' troubleshooting tool on the system. Please type Troubleshooting Control Panel onto [Cortana} search box, click on 'View All', and then Power. Run other tools as well, see image below.

Lastly, if it still isn't fix then I suggest you click on "choose what the power button do", change settings to 'Do Nothing', save changes, and then power off system. 

Secondly, you can change the settings in Power Options:

1. At the bottom, left of taskbar,right click windows icon, click on Power Options, and then 'Change When The Computer Sleeps'.

2. Please change settings to 'Never' and then click Saves Changes. Power off computer, disconnect all peripherals, wait about 3 minutes, and then power on system again. If issue is fix, then you can set sleep back to original settings.

One more suggestion:

Run the System file checker. It scan for any corrupted system files that could be causing problems and fix those corrupt files as well.

a) Press Windows key + X key at the same time, select Command prompt (Admin)

b) In the command prompt type the following command: sfc/scannow and press enter

If no corrupted system files were found , then I would suggest you try the following steps:

a) Select Command prompt (Admin)

b) In command prompt, type the following commands and press Enter after each command....  

DISM.exe /Online /Cleanup-image /Scanhealth

DISM.exe /Online /Cleanup-image /Restorehealth

Thanks for this, I tried it and it still happens.

I'll check on the other solutions below.

I did all the solutions, appreciate the suggestions LSUFAN51.

So far it's not sleeping but the screen is flickering or changing resolution a lot.

I extend the display in another monitor by the way, and it the screen keeps on going black and the icons are re-arranging a lot.

 Nikmeister 25 wrote: "I updated all drivers, bios, etc and no avail"

Surprisingly,latest BIOS update didn't fix the problem on the computer. Please click on link below:

Inspiron 7559 displays multiple issues after resuming from sleep

www.dell.com/.../SLN299492

Nikmeister25 wrote: "So far it's not sleeping but the screen is flickering or changing resolution a lot".

:emotion-2:

Please check if the flickering occur in 'safe mode with networking'. To get to safe mode,restart computer, at the  sign-in screen, hold the Shift key down while you select Power & Restart. After computer restarts to the 'Choose an option screen', select Troubleshoot, Advanced options, Startup Settings , and then Restart. After computer restarts, you'll see a list of options, select Safe Mode with Networking. If the flickering stop then I suggest you try the steps in the video below:

https://youtu.be/lhuHwi_9Mpw

EDIT:

I tried the two new solutions you suggested, still experiencing the same issues whether I am in PC Screen only or Extended screen view.

User experience is the screen goes black when I am typing or working on something.  stays black for a a few seconds and I have to press Fn F8 or just wait for the screen to go back to normal where I see what I'm doing.

It still happens quite a lot.

If issue still occur then I suggest you update display adapters from NVidia and Intel sites.

Drivers - Download NVIDIA Drivers

Drivers & Software - Intel

Please expand 'Update your display driver' and try troubleshooting steps in link below:

support.microsoft.com/.../windows-10-troubleshoot-screen-flickering

I did all your suggestions, no luck.

The latest NVIDIA driver has code 43 and conflicts with the Intel driver. i tried the 2nd to the latest driver and still conflicts, under device manager it says the display adapter is not working properly.  I rolled it back and reset my drivers still not working.

Same user experience when I extend the display to another monitor or using laptop alone.

I type or work on something, screen turns black,  then goes back on and my icons are jumbled up and the display itself somewhat resets or refreshes.

If you installed ' all ' drivers then that might be causing the problems on system. It's best to run the 'Guide Me' option on your support page to find drivers for your system. Please click on link below:

How to find Drivers and update them (Official Dell …