This is happening to me, I have changed setting on network adapters, Device Manager item settings, nothing seems to work. It goes into sleep mode then wakes up on its own within a matter of seconds. Same thing with hibernating.
I just upgraded from Windows 7 to 10. The issue here is when sleep or hibernate are clicked, the computer acts like it's going into that mode but actually shuts down instead. Nothing saved. This is a Gateway NV59 notebook. The desktop PC with Windows 10 works fine. It has nothing to do with the "choose what happens when the lid is closed or power button is pushed" settings. I have then all set to sleep.
The fix for mine was unplugging my Logitech Extreme 3D Pro Joystick from the USB port.
It goes to sleep just fine now.
My computer is failing to sleep again and I don't have anything checked or unchecked that would cause it to fail to sleep.
Someone please help!
Update: I fixed my computer by doing a System Restore.
You can always open an elevated command prompt and run the powercfg lastwake command. (Note that there may be a - or / prior to the lastwake. I forget. A quick search will show you the proper way to run it.)
That will show you what last forced your machine out of the sleep mode. Begin troubleshooting from there.
My computer that I've just installed Win 10 on wakes immediately after putting to sleep.
I've tried all things listed in this thread.
I've gone into the event viewer and filtered on Power Troubleshooter in Event sources for waking, and it indicates Unknown Source.
I've check to see that the NW Adapter is set to allow wake, magic packets only.
The Allow Wake Timers in Power settings is set to Important Wake Timers only.
I've disconnected all USB devices just for testing the sleep.
I've run out of ideas. I'll be searching more on Google. But if any other thoughts/suggestions, it's appreciated.
Huh...reading back through my post, I realized I had NOT unplugged all USB items. My keyboard is USB. I unplugged it, and did a sleep with the wireless mouse (which has a USB dongle), and pulled the USB dongle for the mouse, and it went to sleep.
I think I may have something in BIOS about USB wake. I'll check on that now.