It could be a virus or just random corruption or if you are running McAfee AV and Avast AV.
Only one Antivirus should be used. If you want extra security, keep a copy of Malwarebytes Free.
It doesn't conflict.
You can try doing a System Restore to before the problem (personal files and folders are not affected)
If that fails, try a Refresh which again keeps your files and folders.
To get these options can be a bit trick with W8/8.1
You can try powering on and immediately, repeatedly tapping F8 or Shift F8 but the machine's quick boot may have already got under way.
If you do end up in Windows you can also find them in Control Panel.
Or you can boot from the USB Flash Recovery Drive that you should have made or a W8/8.1 DVD
If you don't have them, you can make a USB Recovery Drive or DVD on another machine.
When you boot on the dodgy machine, choose Repair or Advanced or Troubleshoot and find the System Restore and Refresh options.