I have four desktop PC with varying hardware configurations, all between two and three years old, all running Windows 8.1 with Media Center. They were upgraded from Windows 7 to Windows 8 when it was released, then to Windows 8.1. I am a mad updater - so all BIOS, driver and Windows updates are checked for and applied on a regular basis. I would have only occasional sleep problems with Windows 7 and 8 - but I have found this to be not uncommon with Windows of all versions. Mostly the sleep functions worked fine.
After upgrading to Windows 8.1, ALL of the PCs would not automatically sleep. Actually, three of them would sleep automatically if I restarted the PC but did not use it. That is, do nothing on the PC after a restart - not even touch the keyboard or mouse. In this case the PC would then automatically sleep after the sleep timeout period - but not exactly useful. A restart on the fourth PC didn't have the same result - it would not automatically sleep.
Putting the PCs to sleep manually worked fine. And I am not experiencing any other problems with the PCs. Windows 8.1 works perfectly otherwise and I like it.
I now seem to have solved the sleep problem by following two of Ryu Connor's instructions in this thread.
1. Manually start maintenance under Action Center - WinKey+X > Control Panel (Small or Large Icon View) > Action Center > Maintenance > Start Maintenace. Let it complete - this may take quite some time.
2. Under Power Options, select Change plan settings for the active power plan, then select Restore default settings for this plan. Now set the sleep timeout to your desired setting and set any other power plan options you require. I am using the High performance plan and only change the display off timeout, the sleep timeout and set the Require password on wake-up to No. I have left all other plan options at their default settings. Also, my sleep timeouts are generally quite short - 3 minutes on two of the PCs, 5 minutes and 10 minutes on the other two.
3. Restart the PC. Sleep now works perfectly on all my PCs.
I did not make any changes with powercfg or make any other relevant changes. I can't say if just one of the steps alone - forced maintenance or power plan reset - would have had the same result. My testing time was limited and, now that the PCs are all working correctly, I no longer have a problem PC on which to test.
I hope this is helpful. And a big THANK YOU to Ryu.
I read every bit of information on having Windows 8.1 sleep on its own and tried everything that was listed. The only thing that worked is what Graymatter shows in his thread. Run maintenance, restore the power plan, reboot and now my computer sleeps on its own after the one minute I have it set at.
Tried to fix this for a long time and now it works like it is supposed to. I have gone back and one by one undid all the changes I made befor I read this post and it still sleeps. Forget powercfg, IV6 and messing with the network adapter.
Thank You Graymatter and all those that have worked to solve this problem.