Changing your password to solve this problem is likely to only make it worse unless you are sure that the new password has taken effect throughout the system. Sometimes this takes a considerable amount of time. If you changed your password in the last hour, or so, make sure and check to see if the new password is working for the function it is primarily intended for (ftp/shell/etc.)
As for stats, remember that the user must be a "shell" or "ftp" user for it to work - if the user is an "email only" user, they are not authorized to view stats by default (the owner/user must set them up in the Control Panel, at the link provided by Mark).
If none of your user/password combinations work, and you are using the appropriate user's password, you should contact support via the control panel, as it is possible something is "borked" on the Dreamhost end. Good Luck!