Apply the Free Upgrade to Windows 8.1 Update via the Windows Store. It will take a few hours to download (2 GB to 3 GB), install and configure, but no personal files/data or software will be lost, unless it's incompatible. If you cannot access the Windows Store, you may need to switch the Local Account to a Microsoft Account to proceed.
What are your system hardware spec's?
If you're unsure, run
Speccy to find out more and post a screenshot in your next reply.
Are you using ESET NOD32 Antivirus or ESET Smart Security?
Which on-demand scanners do you use? "Anti-Malware" is too vague to understand.