Computer will not enter sleep mode ?

It is a common issue to have a Windows PC (or laptop) suffer from perpetuating insomnia and not enter into power-saving sleep/hibernate mode, even when the appropriate details are set in the "Power Options".

To troubleshoot, try the following:
1. Enter Command Prompt - click the Windows/Search button and type: cmd in the Windows search dialog
2. Type: powercfg -requests
3. Look up and write down any offending processes that may be preventing the computer from entering sleep mode.
4. Navigate to Device Manager (Windows/Search key > type: Device Manager and press ENTER)
5. Find the devices in the list > right-click, choose "Properties" from the menu > Power Management > tick "Allow the computer to turn off this device to save power"

You can also opt to override requests from a certain offending program/process that keep the computer awake. For example, if Google Chrome is the culprit, type the following in command prompt:
powercfg -requestsoverride PROCESS chrome.exe SYSTEM

If you have an audio driver keeping it awake, for example "Realtek High Definition Audio (HDAUDIO\FUNC_01&VEN_10EC&DEV_0900&SUBSYS_104386BE&REV_1000\4&29409009&0&0001)" try:
powercfg -requestsoverride DRIVER "Realtek High Definition Audio" SYSTEM
It is a good idea to use the entire name of the driver excluding only the content in parenthesis, using partial names may not work.

To see a list of overrides, simply use: powercfg -requestsoverride

It is worth to try updating the Video/Audio/Network adapter/USB drivers to the latest from the manufacturer, as they are often the culprit, or if you know which one is preventing the computer from sleeping.


Other options worth a try if your computer wakes up on its own
To see what woke your computer from sleep mode last time, use:
powercfg -lastwake

- If the network adapter is turning your computer on, look into it's properties under "Power Management", and turn off any options for "Wake on Magic Packet", "Wake on Pattern match", etc.
- It may be worth trying to disable wake timers in the computer under "Power Options"
- In "Task Scheduler", disable Media Center\mcupdate

Notes:
To see a list of hardware devices that can wake your computer, use: powercfg -devicequery wake_armed
To find details about all powercfg command switches use: powercfg -?