Windows 8.1 Does Not Go To Sleep / Standby Automatically

I recently did a clean install of Windows 8.1 Pro x64. Before doing the clean install, all hardware being identical, my Windows 8 was ran smoothly and went to sleep fine automatically after 8 minutes, and 20 minutes later into hibernation.

Now, after the clean install, although I believe I have installed and set up everything as before, the computer does not reach standby automatically anymore. I do not seem to be able to figure out why this is, or how my configuration is different than before. I do not mean to claim that it's Win 8.1's fault (I hope it isn't, because otherwise it would mean that the solution is out of my hands), but it is much more likely that during the lengthy clean install, program installation and configuration process some things have ended up being set up differently than before.

I'd like to figure out how to approach the solution-finding process in a systematic manner as obviously there are many possible culprits that I would like to eliminate one by one. For example, you can find many single tips on the web on this subject, but we would rather need a clear to-do list of what to check. E.g., how can the event logs be used to find the error?