how to start operating system in a safe mode?

Windows into Safe Mode, then a limited number of the necessary drivers and applications are loaded. Because then reduce the risk of system crashes. Usually operating system make to protect from viruses or any work time operating system in Safe Mode, users load the operating system. However, many computer operating system in Safe Mode has always been to secure the load. If you want your computer operating system is always 'Safe Mode' to be loaded, then Follow

StrartMenu

Run

msconfig

System Configuration

BOOT.INI

/SAFEBOOT

MINIMAL

Apply then press the OK button 

Then when you turn on the computer, the operating system will be launched in Safe Mode all the time; Much of which will protect your PC from viruses.