Why won't my computer go to sleep automatically?

To answer my own question, it seems that to discover what's preventing your system from sleeping, you can run powercfg -energy and let it do a trace. The resulting report revealed the following for me:

Which lead me to:

My current testing suggests that this problem is (or can be) caused by running processes.

When running powercfg /requests two processes were listed under the SYSTEM category:

• Print Spooler
  was trying to still print a document

• Windows Media Player Network Sharing Service
  was waiting for playback instructions

After shutting down both services, the system hibernated as expected.

Regarding \FileSystem\srvnet, I found the thread Not sleeping due to : \FileSystem\srvnet which suggests that this is also related to media sharing.

Finally went to: Control Panel\Network and Internet\Network and Sharing Center\Advanced sharing settings

And under media streaming - blocked all - and that did the trick! I don't know if there's another way to allow streaming and enable sleeping, but for now, beats running all night long after waking for a time update etc... :-)

There are several things to check:

• Power configuration of course
• Task scheduler
• automatic wake up for maintenance (network wake up)

I assume your computer is up to date. As you have found that no requests exist, it could not be an interrupt which is causing this. However, its better to check BIOS settings and device manager settings to know which settings and which devices are configured to interrupt. Plus a compatible BIOS update is necessary to let interrupts function accurately.

Besides that, there are problems with multimedia players such as VLC. If it was running, the computer will refuse to sleep. A small piece of software can be found here (which may or may not assist you since you have Windows 8. It works with Windows 7 though).