Backed my working system (10.12.5 with all its updates) using SuperDuper (registered version). Tried to use the App Store but for some reason it got stuck at around 250 MB so I downloaded the combo file via the first post in this thread. The update went as smooth as possible! Sleep works (it takes at least 30 seconds), shutdown works, reboot works and sound works. My system:
Gigabyte Z77N-WIFI
Intel i3 CPU
Intel Graphics 4000
Thanks again for everyones contribution and for the gurus in this site!!!