In Windows, Safe Mode is diagnostic mode where the operating system loads as few executable modules as possible and usually disables devices, except for the minimum necessary to display information and accept input. Under Safe Mode, Windows has reduced functionality, but the task of isolating problems become easier because many non-core components are disabled.
To get into the Safe Mode, press and hold the F8 key as the computer is booting, which should bring up the "Windows Advanced Options Menu".
Sometimes due to disk corruption, file error and even virus infection, Windows might refuse to boot into safe mode. SMFixer is a freeware utility designed to fix issues when the computer cannot boot into Windows Safe Mode.
The program which works on Windows XP, Vista and 7, is simple to use – just run the executable, and click the FIX button and your computer will restart immediately. During restart hit F8 key and you should be able to load Safe Mode.