I have been thinking about this and decided I would not even know where to start. Could it be that something on your system will not allow sleep or is something missing, or just not running...
I have seen some suggestions about a graphic driver being involved, but nothing definite, so I will suggest you open an Administrative command prompt and run two commands. Let them finish and for the second one, copy the html file it makes to the desktop to read. You will receive USB warnings on the powercfg listing, but they may not be involved. Maybe one of these two utilities will provide some guidance.
sfc /scannow
powercfg -energy
It may be something related to your ACPI drivers.