Lost passeord.

I have Ununtu 16.04 . I loaded it on a Toshiba M70 and it was too slow. I tried fitting the HD to a CompaqCQ58 and it booted up quite easily.The only thing is I have now forgotten my password. I downloaded a video for YT on resetting the password. When it came to entering the new password,it did not appear on screen, not even asteriskes. I thien do the repeat password but it aagian does not appear.
What should I do?