Question PC not going into sleep mode - fan actually accelerating

[ivanhoe]

I have recently had to a clean reinstall of Windows 10 on a 5 year old PC (high spec'd in the day so still very functional). When I put it into sleep mode I can hear the fan accelerate and then it just gets stuck like that - the fan runs, it never turns off. The screen, keyboad and mouse all seem to go off, but the fan keeps running. It can't be woken from that mode, I have to restart using the power or reset button.

I have googled this for hours - tried changing all sorts of options e.g. disabling windows fast start, various advanced power options. Some posts suggested the speeding fan sounds more like hibernation - but I have disabled every hibernation option I could find, it should only be sleeping. I've looked in power options in the BIOS but can't see any settings there that I could see having an impact. I'm at a loss - any suggestions?

 

[Lutfij]

Let's start with the specs to your system. List them like so:
CPU:
Motherboard:
Ram:
SSD/HDD:
GPU:
PSU:
Chassis:
OS: Including the version

Which version of BIOS are you on at the moment?

 

[ivanhoe]

Here are the specs to my system.:
CPU: Intel Core i7 3770
Motherboard: Gigabyte GA-Z77X https://www.gigabyte.com/Motherboard/GA-Z77X-UD5H-rev-11#ov
Ram: 32MB Kingston HyperX
SSD: Intel 520 Series 240GB
HDD: 2 x Western Digital 2TB Disks
GPU: Gigabyte GTX650
PSU: Corsair HX750W
Chassis: Antec Solo II Tower
OS: Including the version Windows 10 Home

Which version of BIOS are you on at the moment?
For the above motherboard I am on F8. Bios versions go up to F14 - then Beta versions go up to F16j. Are Beta versions safe to install?

 

[ivanhoe]

Although - a better question may be - do I need to worry about a desktop PC going to sleep? The setting to turn off the screen works fine, isn't that the main thing?