Package has no installation candidate

Question

I have an Ubuntu 15.04 and every time I try to download something (using sudo apt-get install), it says:

Reading package lists... Done
Building dependency tree       
Reading state information... Done
Package <packagename> is not available, but is referred to by another package.
This may mean that the package is missing, has been obsoleted, or
is only available from another source

E: Package '<packagename>' has no installation candidate

I have tried "sudo apt-get update" and it said at the end:

W: Failed to fetch http://ppa.launchpad.net/irie/blender/ubuntu/dists/vivid/main/binary-amd64/Packages  404  Not Found

W: Failed to fetch http://ppa.launchpad.net/irie/blender/ubuntu/dists/vivid/main/binary-i386/Packages  404  Not Found

E: Some index files failed to download. They have been ignored, or old ones used instead.

I have also checked whether all of the checkboxes from "Ubuntu Software" tab of the "Software and Updates" window have been selected, and tried "sudo apt-get upgrade", but none of them worked.

Also, here is my sources.list file, which seems fine:

# deb cdrom:[Ubuntu 15.04 _Vivid Vervet_ - Release amd64 (20150422)]/ vivid main restricted

# See http://help.ubuntu.com/community/UpgradeNotes for how to upgrade to
# newer versions of the distribution.
deb http://old-releases.ubuntu.com/ubuntu vivid main restricted

## Major bug fix updates produced after the final release of the
## distribution.
deb http://old-releases.ubuntu.com/ubuntu vivid-updates main restricted

## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu
## team. Also, please note that software in universe WILL NOT receive any
## review or updates from the Ubuntu security team.
deb http://old-releases.ubuntu.com/ubuntu vivid universe
deb http://old-releases.ubuntu.com/ubuntu vivid-updates universe

## N.B. software from this repository is ENTIRELY UNSUPPORTED by the Ubuntu 
## team, and may not be under a free licence. Please satisfy yourself as to 
## your rights to use the software. Also, please note that software in 
## multiverse WILL NOT receive any review or updates from the Ubuntu
## security team.
deb http://old-releases.ubuntu.com/ubuntu vivid multiverse
deb http://old-releases.ubuntu.com/ubuntu vivid-updates multiverse

## N.B. software from this repository may not have been tested as
## extensively as that contained in the main release, although it includes
## newer versions of some applications which may provide useful features.
## Also, please note that software in backports WILL NOT receive any review
## or updates from the Ubuntu security team.
deb http://old-releases.ubuntu.com/ubuntu vivid-backports main restricted universe multiverse

deb http://old-releases.ubuntu.com/ubuntu vivid-security main restricted
deb http://old-releases.ubuntu.com/ubuntu vivid-security universe
deb http://old-releases.ubuntu.com/ubuntu vivid-security multiverse

## Uncomment the following two lines to add software from Canonical's
## 'partner' repository.
## This software is not part of Ubuntu, but is offered by Canonical and the
## respective vendors as a service to Ubuntu users.
# deb http://archive.canonical.com/ubuntu vivid partner
# deb-src http://archive.canonical.com/ubuntu vivid partner
deb http://www.openprinting.org/download/printdriver/debian/ lsb3.2 contrib

Also, I know that there are other questions similar to this one, but none of the solutions worked for me.

Edit:

As I saw, many people in the comments suggested that I change the 'archives.ubuntu.com' lines in the sources.list to 'old-releases.ubuntu.com' because I have an outdated Ubuntu version. I tried that and the same message pops up when I type 'sudo apt-get update' (some index files failed to download), and when I try to install a package the same thing happens.

Some other people in the comments suggested that I upgrade to a newer Ubuntu version, which I tried also (sudo do-release-upgrade), but at the end it says:

Cannot upgrade, an upgrade from 'vivid' to 'xenial' is not supported with this tool.

I've also tried upgrading using sudo do-release upgrade -d, but then it says:

Checking for a new Ubuntu release
No new release found

Solution

I fixed it by myself. I followed a bunch of people in the comments' advice by replacing 'archives.ubuntu.com' links in the sources.list file with 'old-releases.ubuntu.com' and also deleted a bunch of out of date repositories that were preventing me from executing 'sudo apt-get update'.

Comments

[multithr3at3d]

Ubuntu 15.04 is past end-of-life; I suggest that you update to a supported version.

[Chai T. Rex]

This answer shows how to upgrade to a supported version. Note that LTS versions last the longest (five years for Ubuntu, so 16.04 LTS will last until April 2021) if you want to avoid upgrading so much.

[Kailee Zhang]

Tried the solution to upgrade to a newer version in the link, but it says 'Cannot upgrade, an upgrade from 'vivid' to 'xenial' is not supported with this tool. '

[guiverc]

The standard 'release-upgrade' tool will jump from 14.04LTS to the next LTS version which is 16.04LTS. For non-LTS versions; your 15.04 should become 15.10, then 16.04LTS. Many people decide to just re-install rather than in your case two-jumps. (15.04 = 2015.April release; LTS releases are even.year.April only)

[guiverc]

If you look at archive.ubuntu.com/ubuntu/dists in a browser you'll note no distro titled 'vivid' (it's not supported. You could change it references to old-releases.ubuntu.com/ubuntu/dists which will allow you to add software; but PLEASE NOTE this is not the secure option!