Boot from a Linux USB stick.

Mount the original root filesystem:
Code:
mkdir /x
mount /dev/sda1 /x  ## replace sda1 with actual device)
chroot /x bash
mount /proc /sys 
passwd root
## enter a new root password

passwd user1
## enter a new user1 passwd (replace user1 with real userid)

exit
umount /x/*
umount /x
reboot