Safe mode is a "Minimal" configuration of Windows. Basically it runs
and omits 3rd-party drivers and applications. Think of it as a "Fresh"
install where nothing you've added runs. There are variations of Safe
mode such as 'with Networking' and 'Last Known Working Config'.
To access you repetitively press F8 at 1/2 second intervals to get XP
to stop at the Safe Mode menu and wait for your selections. There is
a short period of time from power ( Just past BIOS boot Screen )
where the system will detect the key press for Safe Mode.