How to disinfect a PC in Safe Mode

Use the following procedure to disinfect a PC with a common virus such as a background app affecting system processing or a registry hack. (This procedure won't resolve issues with a boot sector virus which will likely require a special boot CD or reformatting of your hard drive.)

Steps to start the computer in the 'Safe Mode with Networking'

1. Click 'Start' and then click 'Shut Down.'
2. In the drop-down list of the 'Shut Down Windows' dialog box, click 'Restart,'' and then click 'OK.'
3. As your computer restarts but before Windows launches, press 'F8.' On a computer that is configured for booting to multiple operating systems, you can press 'F8' when the boot menu appears.
4. Use the arrow keys to highlight the appropriate Safe Mode with Networking option, and then press 'ENTER.'
5. Please log on to Administrator account. If you are unable to log in as 'Administrator' (if you are not aware of an administrator password) please log in as a Normal User (Normal User Account).
6. If you have a dual-boot or multiple-boot system, choose the installation that you need to access using the arrow keys, and then press ENTER.

You will now get a screen in your Desktop with the word 'Safe Mode' written on the four corners.
The next step to be done is to run an Online Safe Mode Scan.

Running the Safe Mode Scan

1. Visit: www.microsoft.com/security/scanner/en-us/default.aspx
2. Click "Accept" on the Service Agreement."
3. Click "Install Now" button.
   NOTE: If installation is unsuccessful, click on the information bar below the address bar then click "Install ActiveX Control"
4. When a Security Warning dialog box appears, asking you if you want to install the Windows Live Safety Center Component scanner, please click "Install".
5. Click on "Launch Scanner" button.
6. A secondary windowpane opens up titled Full Service Scan.
   a. Click on "Next" to proceed with the complete scan.
   b. A progress bar will appear showing the status of the scanning tools while it's downloading.
   c. A Status: Scanning your computer appears with
   - Virus and spyware scan
   - Registry Cleaner Scan
   - Disk Cleanup scan
   - Disk Fragmentation Scan
   - Open Ports scan
   - Computer information
   d. After the scan, click on "Next" on the summary page.
   e. Status Window: Fixing process will start.
   f. Summary page will appear. Click on "Next".
   NOTE: Share information with Microsoft has a check by default.
   g. Uploading report with Microsoft will proceed.
   h. You will see a message "Scan is done."

Now restart the computer in the Normal Mode by the following steps:

1. Click 'Start' and then click 'Shut Down.'
2. In the drop-down list of the 'Shut Down Windows' dialog box, click 'Restart,'' and then click 'OK.'

Finally -- Make sure an anti-virus app is installed and running with current updates on every PC. Windows Defender is included with Windows 7/10.

Note: If the virus has disabled functions like Windows Firewall, Security Center, and System Restore points, and you are running Windows 7, there are extra steps required. First reboot PC with F5/F8 to get to boot menu, select the Repair option, when repair completes reboot PC normally, then insert original Windows 7 DVD and select Setup.exe followed by Upgrade option. This will not clear any existing programs or data but it will restore the missing or corrupted Windows registry entries. Once restored, reboot as normal and run Windows Updates. Finally check to make sure an anti-virus is installed and the firewall is active. 

99% of all viruses are contracted through user interaction (self-inflicted). DON'T download or install apps from unrecognized sources while web browsing or opening email attachments. One click on a bad email or web page link is all it takes to infect your PC.