Locked Computer Help!

My boss has an older HP pavilion computer that he changed the administrator password on a few months ago, and now can't remember what the password is. I need to try to get onto the computer without losing the files that are on the computer. I have access to another, non-administrator account on the computer, but when I try some of the tricks I've found online, unfortunately I need to put in the administrator password to access the settings needed. If anyone can help me try to get on to the computer without losing the files it would be greatly appreciated.
Thanks all,
Walshy