Somehow an aberration entered my password settings. When get box asking for password and give correct one, upon presseng enter the box jiggles from left to right, then says is incorrect and repeats request.
Have changed password via direct input, but get same result. Any ideas?

Keyboard layout? Do you see correct letters if you enter your password in the username field?

first of all, maybe your CAPS LOCK IS ON?

then, can you open a terminal window and start the same app with sudo? does it accept your password then?

Tried with caps, with other key set [use dvorak], with all possible misspellings and mistakes, and did use boot time settings to change password [and got response: password changed]. This shaking from side-to-side just after enter ENTER with password is something have never seen before and makes me believe it isn't any mistake on my part, but the software refusing to act on the given password -- ANY password; so am locked out of control center, and with the 'upgrade' I did to new version hoping that would fix it and still retain my files, am now locked out of everything, as upon boot am immediately given login request for password, which of course it refuses to accept. Never experienced or heard about anything like this, so hope this gets a lot of views, because it's going to take someone with a lot of experience to figure this out.

Or not.

I have had instances where if the O.S had an issue booting it would not accept the correct pw. Have you tried to log in with a terminal not running x? I would look at the boot logs and also check the permissions of needed directories to see if they are set to the correct owner and privileges.

+1
Ctrl-Alt-F2 (or 1-6; F7 to get back) and login with username and password -- have you tried it, yet?

Why indeed I have.

this:or any other way to start troubleshooting or narrowing it down, systematically.
never say never.

Who's on first? Is williamvw the OP or not? LOL
OP?

Have tried Ctl-Alt-F2, but still refuses to accept my password, and of course can't get to the boot logs and permissions [at least don't think so without the password].
Likewise can't work in terminal window without password, and sudo gets same obstruction.

There should be boot options to store the log or view it better ,manual boot anyways. A password is not required for this.

if you really can't get into your system at all then there's only one solution, no?
try to save what you can and reinstall.
otherwise, please give us something to work with.
http://www.catb.org/~esr/faqs/smart-...html#beprecise

Don't reinstall the OS due to a password issue! Boot the system to single user mode and reset the password. This is a fairly simple procedure.

What distro and version are you running?

Used Frenzy to get to single user and for change of root password; all went well and got new password installed -- BUT, it made no difference and when asked for password and entered the new one, still refused to accept it.
Believe problem isn't that am entering a wrong password [always knew it was correct], but that for some reason the program is refusing to allow ANY password to be processed.
Any suggestions [apart from 'new install']???

Just a way out guess but With laptop keyboards that are also a combination number pad something might be turning on/off the num lock. So what you think you are typing might be numbers instead of letters.