Hello, all. I am still a relative newbie. I started out with Mandrake 10, then 10.1, and then I tried Mandriva Professional. That was an unsavory experience, so I looked around for another distro. My son has more exp. with the various flavors of linux, so I more or less listened to him extol the virtues of Kubuntu. I am running that now.
Everything was fine until one day Firefox would not load. I thought that possibly it was because I had forgotten to run the system update routine. On running it, some of the Firefox files must have become corrupt, because I can neither remove nor install Firefox. I looked around on Mozilla's site for some info, and also on Kubuntu's, to no avail. Since I don't know if the problem I am having is Firefox-related, or Kubuntu-related, I just don't know how to proceed.
I really like Firefox and would like to use it, but at this point it looks like I may have to reinstall Kubuntu in order to get everything working again. This is just a guess on my part, so if anyone knows a better approach to solve the Firefox issue, please by all means reply.
My installation is an Athlon EXP with 256 Mb of RAM, with Kubuntu 5.04 Hoary. I am not sure what version the Firefox was.
Any help will be most appreciated.

Bighooked

When you say it won't start, do you mean it looks as if it's going to start but then stops again or that you get some kind of error?

What happens when you type this into a terminal? What happens when you type this? What happens when you type this? Don't just describe what happens when you type this in the terminal. Copy and paste exactly what errors or messages you get afterwards.

Thanks for your help.

On typing in firefox in a teriminal, nothing happens (expected). I had previously removed firefox so that I might have been able to re-install it.

Typing in mozilla-firefox yields the same result.

Here is the output from sudo apt-get update:
Ign http://ubuntu-backports.mirrormax.net hoary-backports Release.gpg
Ign http://ubuntu-backports.mirrormax.net hoary-extras Release.gpg
Ign http://ubuntu-backports.mirrormax.net hoary-backports Release
Ign http://ubuntu-backports.mirrormax.net hoary-extras Release
Ign http://ubuntu-backports.mirrormax.net hoary-backports/main Packages
Ign http://ubuntu-backports.mirrormax.net hoary-backports/universe Packages
Ign http://ubuntu-backports.mirrormax.net hoary-backports/multiverse Packages
Ign http://ubuntu-backports.mirrormax.net hoary-backports/restricted Packages
Ign http://ubuntu-backports.mirrormax.net hoary-extras/main Packages
Ign http://ubuntu-backports.mirrormax.net hoary-extras/universe Packages
Ign http://ubuntu-backports.mirrormax.net hoary-extras/multiverse Packages
Ign http://ubuntu-backports.mirrormax.net hoary-extras/restricted Packages
Err http://ubuntu-backports.mirrormax.net hoary-backports/main Packages
404 Not Found
Err http://ubuntu-backports.mirrormax.net hoary-backports/universe Packages
404 Not Found
Err http://ubuntu-backports.mirrormax.net hoary-backports/multiverse Packages
404 Not Found
Err http://ubuntu-backports.mirrormax.net hoary-backports/restricted Packages
404 Not Found
Get:1 http://ubuntu-backports.mirrormax.net hoary-extras/main Packages [2490B]
Get:2 http://ubuntu-backports.mirrormax.net hoary-extras/universe Packages [2411B]
Get:3 http://ubuntu-backports.mirrormax.net hoary-extras/multiverse Packages [33B]
Get:4 http://ubuntu-backports.mirrormax.net hoary-extras/restricted Packages [4182B]
Get:5 http://us.archive.ubuntu.com hoary Release.gpg [189B]
Get:6 http://us.archive.ubuntu.com hoary-updates Release.gpg [189B]
Get:7 http://archive.ubuntu.com hoary Release.gpg [189B]
Get:8 http://security.ubuntu.com hoary-security Release.gpg [189B]
Ign http://kubuntu.org hoary-updates Release.gpg
Hit http://us.archive.ubuntu.com hoary Release
Hit http://archive.ubuntu.com hoary Release
Get:9 http://security.ubuntu.com hoary-security Release [16.9kB]
Ign http://kubuntu.org hoary-updates Release
Get:10 http://us.archive.ubuntu.com hoary-updates Release [16.8kB]
Ign http://kubuntu.org hoary-updates/main Packages
Hit http://archive.ubuntu.com hoary/multiverse Packages
Get:11 http://kubuntu.org hoary-updates/main Packages [77.0kB]
Hit http://archive.ubuntu.com hoary/multiverse Sources
Hit http://us.archive.ubuntu.com hoary/main Packages
Hit http://us.archive.ubuntu.com hoary/restricted Packages
Hit http://us.archive.ubuntu.com hoary/main Sources
Hit http://us.archive.ubuntu.com hoary/restricted Sources
Hit http://us.archive.ubuntu.com hoary/universe Packages
Hit http://us.archive.ubuntu.com hoary/universe Sources
Get:12 http://security.ubuntu.com hoary-security/main Packages [70.8kB]
Hit http://security.ubuntu.com hoary-security/restricted Packages
Get:13 http://security.ubuntu.com hoary-security/main Sources [15.5kB]
Hit http://security.ubuntu.com hoary-security/restricted Sources
Hit http://security.ubuntu.com hoary-security/universe Packages
Hit http://security.ubuntu.com hoary-security/universe Sources
Hit http://us.archive.ubuntu.com hoary-updates/main Packages
Hit http://us.archive.ubuntu.com hoary-updates/restricted Packages
Hit http://us.archive.ubuntu.com hoary-updates/main Sources
Hit http://us.archive.ubuntu.com hoary-updates/restricted Sources
Fetched 206kB in 2s (75.7kB/s)
Failed to fetch http://ubuntu-backports.mirrormax.ne...86/Packages.gz 404 Not Found
Failed to fetch http://ubuntu-backports.mirrormax.ne...86/Packages.gz 404 Not Found
Failed to fetch http://ubuntu-backports.mirrormax.ne...86/Packages.gz 404 Not Found
Failed to fetch http://ubuntu-backports.mirrormax.ne...86/Packages.gz 404 Not Found
Reading package lists... Done
E: Some index files failed to download, they have been ignored, or old ones used instead.

Here is the output from typing in apt-get install firefox:
Reading package lists... Done
Building dependency tree... Done
Suggested packages:
firefox-gnome-support latex-xft-fonts xprint
The following NEW packages will be installed:
firefox
0 upgraded, 1 newly installed, 0 to remove and 1 not upgraded.
Need to get 0B/8956kB of archives.
After unpacking 25.3MB of additional disk space will be used.
WARNING: The following packages cannot be authenticated!
firefox
Install these packages without verification [y/N]? y

Preconfiguring packages ...
(Reading database ... 67819 files and directories currently installed.)
Unpacking firefox (from .../firefox_1.0.6-1ubuntu1~5.04ubp1_i386.deb) ...
dpkg: error processing /var/cache/apt/archives/firefox_1.0.6-1ubuntu1~5.04ubp1_i386.deb (--unpack):
trying to overwrite `/var/lib/mozilla-firefox/extensions.d/00classic', which is also in package mozilla-firefox
dpkg-deb: subprocess paste killed by signal (Broken pipe)
Errors were encountered while processing:
/var/cache/apt/archives/firefox_1.0.6-1ubuntu1~5.04ubp1_i386.deb
E: Sub-process /usr/bin/dpkg returned an error code (1)

I am assuming that the miriad error messages indicate that there is a problem, but exactly what that is, I don't know. I have not made any directories read only, which might serve to prevent new software installations.

Thanks for your help again.