Looking at your Speccy log your hardware all looks good, this suggests a software issue which will take a bit of investigation.
You are using Kaspersky AV, is this a paid for product or a free or trial version, we may need to temporarily uninstall it for testing purposes.
First thing that I suggest you try is booting the computer into Safe Mode only and then try using the computer for the most basic of things, if no shut down, restart the computer in Safe Mode with Networking repeat the same types of use as in Safe Mode only but this time also try connecting to the internet, post back with an update for us when both of the above have been tried, how to boot into Safe Mode in Windows 8.1 here
An explanation of what we are attempting to achieve by doing the above; when booting into Safe Mode only the bare minimum amount of drivers are loaded, if the computer runs ok in Safe Mode we then try Safe Mode with Networking to see if the computer still runs ok, if it does it suggests that network card and internet service are ok and that another service is causing the problem, AV programs and their drivers are one of the most common causes of conflicts and that was why I have asked about Kaspersky above.