Reinstalled a video driver from Dell, restarted PC and Sleep is now an option.
Later, the PC does not stay in Sleep mode. I noticed the same in Hibernate, did not stay in that mode either.
Now on...

already tried that

I am looking in old style Control Panel, only shut down and hibernate are offered in Power Options with "change settings that are currently unavailable". No option for adding Sleep

I installed Win10 yesterday on my desktop, but sleep is not an option on power menu. Have tried all options that I find in various forums including driver updates and system settings, but can not get...