I had to remove a new kernel version after Ubuntu refused to boot. Since then the update manager has not been working and I get the following error. How do I get the update manager to work again?
W: The repository 'http://ppa.launchpad.net/kernel-ppa/ppa/ubuntu xenial Release' does not have a Release file.
N: Data from such a repository can't be authenticated and is therefore potentially dangerous to use.
N: See apt-secure(8) manpage for repository creation and user configuration details.
W: The repository 'http://ppa.launchpad.net/tiheum/equinox/ubuntu xenial Release' does not have a Release file.
N: Data from such a repository can't be authenticated and is therefore potentially dangerous to use.
N: See apt-secure(8) manpage for repository creation and user configuration details.
W: http://archive.canonical.com/ubuntu/dists/precise/Release.gpg: Signature by key 630239CC130E1A7FD81A27B140976EAF437D05B5 uses weak digest algorithm (SHA1)
E: Failed to fetch http://ppa.launchpad.net/kernel-ppa/ppa/ubuntu/dists/xenial/main/binary-i386/Packages 404 Not Found
E: Failed to fetch http://ppa.launchpad.net/tiheum/equinox/ubuntu/dists/xenial/main/binary-i386/Packages 404 Not Found
E: W: Some index files failed to download. They have been ignored, or old ones used instead.
You're trying to get content of repos for xenial Ubuntu distribution (16.04) but if you go for example to http://ppa.launchpad.net/kernel-ppa/ppa/ubuntu/dists/ you can see that xenial is not available for this ppa/. Did you system upgrade to 16.04 recently?
It doesn't have anything in common with removal of kernel.