Assuming Win8.1 64-bit...
Please answer each of the following [admittedly tedious] diagnostic questions in a correspondingly-numbered list in your very next reply, preferably without quoting this post:
1a. When (approx. date) did you purchase the computer?
1b. Did the computer come with Win8 (or Win8.1) preinstalled, did you do a clean install of Win8 (or Win8.1), or did you upgrade a (e.g., Win7) computer to Win8?
1c. Who manufactured the computer (e.g., Dell; HP; Lenovo; Acer)?
1d. Have you ever done a Refresh? ...a Reset?
1e. Has Windows 10 ever been installed?
2a. Assuming a third-party anti-virus application/security suite is NOT installed => What Definitions versions are currently listed in Defender's Update tab?
2b. What Definitions last updated date?
2c. What happens when you click on the UPDATE button on that tab?
- What third-party anti-malware applications (i.e., not Windows Defender!) are installed, if any? What third-party firewall, if any?
- Has a(nother) Norton application or a McAfee application EVER been installed on the computer since you bought it?
- Have you ever run the Norton Removal Tool and/or the McAfee Consumer Products Removal Tool?
- What Update Version & KB number are displayed in the second line of text in IE11's Help | About [Alt+H+A] tab; e.g., Update Version: 11.0.54 (KB1231231) ?
- Is Adobe Flash Player v26.0.0.137 installed? TEST HERE USING INTERNET EXPLORER ONLY! => http://www.adobe.com/software/flash/about/
- Is Firefox version 54.0.1 (or higher) and/or Google Chrome version 59.0.3071.115 (or higher) or any other alternate browser installed?
- Are you in the habit of using "Registry cleaners" (e.g., Registry Mechanic; System Mechanic; RegCure; RegClean Pro; Advanced SystemCare; Total System Care; Glary Utilities; Registry Booster; McAfee QuickClean; AVG Quick Clean; AVG PC TuneUp; Norton Registry Cleaner; Norton PC Tuneup; PCTools Optimiser; Bitdefender OneClick Optimizer; SpeedUpMyPC; FixMyPC; PC Doctor; TuneUp Utilities; WinMaximizer; WinSweeper; Comodo System Cleaner; Advanced System Optimizer; CCleaner Registry Cleaner component)?