First check Power Settings in Control Panel for anything unusual.
Check System Properties/Advanced/Startup&Recovery .. Try unchecking all at lower part of panel and checking 'none'
Start up and go into Bios and check settings in there.
Let us know what you have found.
I just had this myself. PC always starts at some point after I put to sleep.In the end I got fed up with it and looked it up on theHP Forum.
The Forum had the answer.
Go to
Start
Device manager
and enter Properties for those items that make it start
disable "Allow device to start computer" in Power Management.
Mouse
Keyboard
Nework Adaptor
All or one of these is causing your problem.
I am now sorted.