Please do the following:
1. Please open Internet Explorer and click Tools -> Internet options.
2. Please click on Connections tab.
3. Click LAN Settings… and a window named LAN Settings will open.
4. Please uncheck all options and click on Ok.
5. Please close Internet Explorer window.
Then, Start > Run (or search for Vista/7) > MsConfig > Start up, See if you can find anything weird or unusual there.
Pleaserun McAfee stinger on your computer in safe mode and follow the step as guidedby ConorD62. Restart the computer and manually update McAfee and run a fullscan. It may fix the issue on your computer.
Howto use stinger: