Recently I upgraded to Windows 10 LTSC 2021 and got a new graphics card (RTX 3060), and since then my computer has been intermittently having this problem. Sometimes when I tell Windows to shut down, it logs me off and turns off the screens but leaves the system running for about 20 more minutes with a small amount of disk activity. Twice it has stayed running all night with no disk activity and I had to hold the power button to turn it off. If it happens when I try to sleep or hibernate instead of shutting down, it will do the same thing and end up turned off instead. I've tried looking in the event viewer and don't see anything suspicious from the times this happened, just an error saying the last shutdown was unexpected. It doesn't seem related to what I do, since I've tried changing up my routine and done all the normal stuff in both sessions that ended with the failed shutdown and sessions that shut down/slept/hibernated properly. Some things I've tried are: Turning off fast startup. That made no difference other than making the event viewer stop saying the shutdown was unexpected after it eventually turns off. It also predictably has no effect on sleep or hibernate. Shift+clicking Shut Down. That did nothing. Making sure all drivers are up to date and Windows doesn't have any updates waiting to install. Making sure there aren't any power-related settings in the BIOS that may need changing. Doing different parts of my routine at different times and shutting down afterwards. I've now done everything in both sessions that fail to shut down and sessions that shut down normally, so it doesn't seem related to what I do. Shutting down the PC more often to reduce the number of variables with what happened while it was running. It always seems to shut down properly after running for 2 hours or less. So far I've only seen it fail to shut down after roughly 10-11 PM, but it's hard to see if the time actually means anything or not. That's still well within the active hours I set in Windows. Logging off before shutting down. So far it hasn't failed to shut down after logging off, but I haven't done it enough times to be confident it actually makes a difference. I initially thought it was related to the RTX 3060 I installed since it didn't happen during the 2-3 days I was on Windows 10 using integrated graphics before installing that, and it first happened the next day. I also thought it might be some kind of hardware or driver conflict between a 2021 graphics card and a 2014 CPU and motherboard (i7 4790k on an MSI Z97 Gaming 5). After some testing in the weeks since then, it seems to happen infrequently enough that I now doubt it's hardware related, but I'm still not sure. At this point I have a feeling it's related to something Windows is doing in the background, possibly scheduled sometime during the 10 PM hour, but I have no idea how to figure out what that might be or fix it. I could really use some advice from someone more knowledgeable about what might be going on or how to diagnose stuff like this. Update: After digging through a few crash dumps I saw that one time it was caused by the integrated graphics driver rather than the Nvidia driver. After numerous other solutions failed, I tried disabling the Intel HD Graphics 4600 in device manager and it has shut down properly ever since. It seems the Nvidia driver is doing something to interface with the Intel graphics and that makes it unable to change power states properly. I'm not very happy with the solution, but I don't actually need to use the integrated graphics for anything so it's fine.
I had a similar issue (e.g. PC wouldn't sleep when I requested it). Turns out, I had my Plex server running in the background. I killed that task and was able to make it sleep. Basically, there's probably some software running in the background that's preventing it from sleeping.
If that's the case, would it still act like everything is working, turn the monitors off, and then just run for a bit and shut down instead of sleeping? I'd think if something was running, Windows would stay on and not start the process. I've also seen something in one of the event viewer logs about a certain process trying to veto shutdowns, but that happens even when everything works fine. I'd think if something was holding it up, there would be a similar event for that.
Ok, with a bit more digging I found that the times it failed to sleep made dump files. After checking those, it seems like the problem is a DRIVER_POWER_STATE_FAILURE due to an IRP timeout in the Nvidia driver for the RTX 3060, so it seems my initial suspicion was right after all. I'll try updating the driver since there's a new version in the last few days and see if that fixes anything.