I decided to take the plunge and upgrade my Dell Optiplex 755 USFF music PC from Windows 7 to Windows 10. The idea of a free upgrade with smaller disk footprint and better security was just too good too pass up. The upgrade went pretty smoothly until about two weeks later.
At first everything seemed to work wonderfully. Then I started to be unable to wake the Dell Optiplex without a reboot. There were also some weird chimes coming from the speakers when the computer was unable to be wakened. The hard drive was working, so it appeared the computer never actually made it to sleep mode. Especially annoying, since this PC provided our streaming music on our patio.
I even went through a complete Windows 10 OS reinstall, to see if that would help. No avail. I tried turning hybrid sleep mode on or off. I applied a BIOS upgrade from Dell. I looked though the event logging and found nothing out of the ordinary.
Currently, I have disable sleep altogether and resorted to mapping my sleep button to the ancient hibernate mode until Microsoft or Dell sorts this out.
UPDATE: Turns out the final solution was to change the settings on USB. Start|Settings|Power & sleep|Additional power settings|Change when the computer sleeps|Change advanced power settings|USB settings|USB selective suspend settings set the setting to "Disabled". After this change sleep seems to work as it should on Windows 10 on the Dell Optiplex 745...