16.04 will not accept password, guest works fine

http://www.psychocats.net/ubuntu/resetpassword

Is site I used. At finish it said I had new password.

OK and when you log in to the system as your user, does the new password work?

Bios password is nothing to do with Ubuntu

Actionparsnip
No, nothing changed. Same as before, I put in new password, a screen comes up with text, for less than a second, then black screen also less than a second. Then to login screen again. Guest works, as before, just click on login. I do not use guest often, but I do not ever remember it needing a password. Sometimes the refresh rate is wrong. So bad I cannot use it, must reboot. There was what I think may be error message. Will post, and give site its on. Getting late here, be back tomorrow. Thanks for answering.
.

This seems not to be a problem with the password, but some kind of crash that logs you off again immediately after logging in.

When did this problem start? After a recent package update?

Can you log in on a virtual terminal (e.g. ctrl-alt-F2)?

Manfred
Yes. I get logged in, there are 22 lines of information. Then ( michael@16:/$ ) and blinking _ after $ sign. Would send picture, but neither Pastebin or Imgur will accept my photos.
In the 22 lines of information, do not know what this means.
           No directory, logging in with HOME=/
           To run command as administrator (user "root"), use "sudo <command>".
           See "man sudo_root" for details.
Problem started two days ago. Three days ago I ran a diagnostics program, from Ubuntu Software Center. Can't remember the name. Only thing I noticed, after program completed, computer would not read USB stick, that I had inserted at request of program. Reads OK on laptop I am using now. After shutdown that day, have not been able to get in. Don't remember an update. Had forgotten this, just remembered, or would mentioned sooner. When I can get some program working, I will send site for pictures. Thanks for answering.

Maybe this is the important hint:
"No directory, logging in with HOME=/"

It seems that something is wrong with your home directory.
If you log on in a virtual terminal and issue the command

ls -l /home

what output do you get?

By the way, to shut down the computer from that mode you can use the command
sudo shutdown now

michael@16:/$ ls -l /home
total 16
drwx------ 2 root root 16384 Aug 6 2016 lost+found

I believe you are right about password. Any time I put incorrect password in, it tells me it is wrong.

Your home directory got lost.

Did you set up a separate partition for home?

What is the output of

df -h | grep '/dev'

(the important information is in the first and last columns, you can ignore the numbers in the size columns)?

guest-gwznbq@16:~$ df -h | grep '/dev'
udev 1.9G 0 1.9G 0% /dev
/dev/sdb1 38G 30G 6.3G 83% /
tmpfs 1.9G 20M 1.9G 1% /dev/shm
/dev/sdb3 45G 52M 43G 1% /home
guest-gwznbq@16:~$

Is this ok, or do I need to do it like #8? --------michael@16:/$

I think you have found the problem. I made a mistake in partitioning, when I originally installed 16.04. Made three partitions. First ( sdb1 ) was set as " / " and flag boot. Second ( sdb3 ) was larger. I usually set as " /home ", but some how didn't. Then made swap partition. Some time ago, went to Gparted, and added " /home " to second partition ( sdb3 ). Do you think if I remove " /home " from second partition ( sdb3 ), it should work correctly? Then enlarge first partition to combine sbd1 and sbd3.

Manfred
Solved!! Your #9 was the answer. The commands above, bottom #11, never worked as I though they should. Studied the site you gave in #11, bit to completed for my old brain. Did the # 2 in your last post, works just fine. I would have never found the problem myself. Thanks a lot.

Thanks Manfred Hampl, that solved my question.