What should you do to completely remove a rootkit from a computer?

A rootkit is a software program that enables attackers to gain administrator access to a system. It is installed by the attackers  on systems when they have been successfully compromised.There are different approaches how to remove a rootkit from a computer.
1. Restart the computer. - the simplest approach. 
2.Open msconfig and enable bootlog.
Click on the Start tab, then Run. Type in “msconfig”  .Go to the “boot.ini” tab and tick “Boot log”.