Reboot the linux
1-Press esc to intruppet boot loader
2-Press e to edit boot loader to load linux Kernal in single mode
3-add s at the end of  of the line and press ENTER

kernel /vmlinuz-2.6.18-194.el5PAE ro root=/dev/VolGroup00/LogVol00 s

3-Press b to boot

4-Linux will boot in single mode
5-now change the password of the root host# passwd root