If you have access to the console and the machine runs GRUB or something similar, reset of a password is easy. Just interrupt the boot before kernel load (hit the Tab key if it really is GRUB you have there), edit the kernel load line, and add the following to the very end:
init=/bin/bash
Then boot that kernel load line (F10 in GRUB) and the machine will come up in single-user ‘bash’ shell, and you can run ‘passwd’.