If you find the answer let me know. My desktop is the same way. I checked everything that is running in the background, no luck. I have a sidebar program that has a button for sleep mode. The only good thing is if I download movies or large files I don't have to set it to not sleep. 

^ This ^ I picked up a lenovo, mostly for word processing and vids.  It won't sleep either.

Count your blessings.  I recently acquired a Dell laptop with Win10Pro and through trial and error have found that sleep is a serious battery killer.  I've re-set all the power settings so that it never sleeps in any circumstances and I can get a good 8 hours of use doing so.  If it sleeps for as little as 15-20 minutes, battery life drops by as much as a third or more - seems completely counter-intuitive, but MS appears to have implemented sleep very poorly in Win10 if it's intent was to preserve battery, which it simply does not.

Mh could be many things:

First logical thing i would do is unplug every USB device connected to the Laptop because it might interfere with sleep.Its important to restart the system after you have unplugged the USB stuff-restart and see if it will go to sleep.
´

Hybrid sleep borked:
"Power Options -> Change Plan Settings -> Sleep -> Allow hybrid sleep -> Setting -> Off" to disable hybrid sleep. 
Dunno about this one but apparently setting it to off will actually turning it on as some describe.
Sounds funny though

Media:
media running preventing the laptop to go to sleep:
System Control\Hardware and Sound\Energy Options\Power Management Settings

Or :
click the notification center on the taskbar (looks like a speechbubble)

click on all settings
Network and energy saving
additional energysettings
there will be a clickable option on the right side of your selected energyplan, that says change energy saving settings, click on that.
Now click on advanced energy settings
Scroll down to the bottom of the list until multimedia... now set the first one to allow sleep.

Chrome:
close it.


 

Guys nothing is plugged in at all except the wireless mouse and it never has caused an issue with other laptops and sleep mode. Hybrid sleep is off, and hibernate is disabled. All programs are closed when I want it to sleep. It still refuses to do so, even after 4 hours. 

https://www.cnet.com/how-to/find-out-what-program-is-interrupting-windows-sleep-mode/

It would have to be Windows ten on the Dell, because when I had a Dell mine never slept after I tweaked my power settings.

Willy, I have a Dell win10 laptop and it goes to sleep whatever time I set it. Don't know. Also have a Dell desktop but that has win 7 on it and 8.

Hit it with a hammer, it will sleep.

Maybe he drinks too much coffiee?

Actually I got it working, I just don't remember how. I think it was the reply from Phoon. I tried that and there was a multimedia app blocking sleep mode. I turned it off, it now works. Thanks guys.