Everything you have said points to one thing to me, a failure to
upgrade from 10.04 correctly. Correcting this has only one fix that's
worth the effort IMHO - erase Ubuntu and start again.

You say you have separate HD's for Ubuntu and Windows so the way to go
would be to disconnect the Windows drive then install Ubuntu 12.04 and
let it take over the entire drive. After that you can plug the Windows
drive back in and boot into the Ubuntu drive to automatically enable
dual-boot.

Once you have 12.04 installed and updated etc you won't have to think
about upgrading the OS for a full 5 years

You can remove software centre from the terminal. Then you should clean the
cache or it will just install the old one again. Then re-install software
centre from the terminal. Have you tried Synaptic?
#purge will remove all traces while remove will leave config files
sudo apt-get --purge remove software-center

#clean removes all packages from the cache, but don't do this if you want
to keep the files (debs), such as you are on dial up
sudo apt-get clean

#download (if you used purge) and install a new one
sudo apt-get install software-center

try also

sudo apt-get install synaptic

I installed 10.04 from a CD, and it also wanted a password. Would not accept the
one I put in on install, so a downloaded upgrade can't be the whole thing.

Here are the instructions, from Ubuntu, on how to change the password even
when you don't kmow it:

https://help.ubuntu.com/11.04/ubuntu-help/user-forgottenpassword.html

I've saved the page and put it in Dropbox.

Reading the whole article - it included wireless. I don't have wifi on the
desktop, but use a cable. We do have WPA wifi. Could Ubuntu have decided that we
need the wireless password anyway?

The funny thing about all this, is I have never saved passwords in a program. I
just copy and paste from a text file which is NOT named passwords. I delete all
history and cookies when I exit a browser. Most of the software on the XP drive
is installed via serial number. No passwords. Ubuntu never asks on a software
install.

I was really pleased when I installed 10.04. Everything just worked.
This included internet, Wacom tablet, mouse, printers (slow from internet is
still driving me nuts)even the old serial port Epson scanner.

I only tried recovery mode after I deleted some sound program using Synaptic,
and the microphone went with it. That's when the password nonsense in recovery
started. I never needed a password to get into the BIOS when the machine was
2K/XP. I had to boot through the BIOS anyway. Safe mode just used F8. So where
Ubuntu got the wrong password from is a real puzzle. The one I did put in works
just fine for any other command.

There is one other possibility - could Ubuntu be picking up computer NAME rather
than password? I think I had a rather profane network name for the computer at
one time.

Are you confusing BIOS with GRUB? You don't boot through the BIOS, although
of course it is involved in the booting process. The menu you see when
starting Ubuntu is the GRUB menu (Grand Unified Boot Loader).

I am not confusing BIOS with Grub. I used BIOS when desktop was 2K/XP to select
the drive the way Grub does now. Ubuntu has overwritten the 2K drive.

The boot menu for Safe mode/Setup etc. comes up before Grub even opens. I have
no idea of how a Ubuntu only or partitioned Windows/Ubuntu drive opens. Never
saw one.

Since the Boot menu shows before Grub, I'm wondering if there is a conflict of
info somewhere on booting up since nothing but online sites and email have ever
had a password. I'm just trying to figure out how Ubuntu set up its own criteria
to begin with so I can avoid it in the future. Like I said - once from CD, once
from download so the error has to be on my computer somewhere.

I don't remember Ubuntu asking for a password on install, only when you opened
Ubuntu for the first time.

Is it possible that the user name is wrong - not the password? Where does Ubuntu
get user name from? It has picked up the computer name right, but the computer
name and user name are different, and user name different again on XP.

Every time I have installed Ubuntu on a PC during the install process I
am asked to input and confirm the password, and at that time I can elect
to have it do an automatic login at boot up so I don't have to as I am
the only user. When I load new apps or use sudo I do have to put in the
password.