When your computer gives problems and you want to identify where is the problem, then you can use the safe mode for this. In safe mode, only limited number of driver programs are enabled. Therefore you cannot use CD drive. You cannot use the printer. And many other unnecessary drivers are not enabled.

While in Safe Mode, you can use the ScanDisk, defrag and other utility programs to repair your computer. You may wonder how to bring the computer to safe mode. When Windows boots up, you have to press the F8 key. You should press the F8 key before the windows screen appears. Then you can choose the safe mode option to boot.
Some Anti virus software will tell you that some viruses can only be removed in safe mode, therefore the antivirus software will automatically start in safe mode or you may have to goto safe mode and then run the virus removal utility to remove the virus.