update's error message

i was trying to make an update and it showed this message ''Again'' :(Could not download all repository indexes

The repository may no longer be available or could not be contacted because of network problems. If available an older version of the failed index will be used. Otherwise the repository will be ignored. Check your network connection and ensure the repository address in the preferences is correct.)

And this was shown in the details :(Failed to fetch cdrom://Ubuntu 10.04.1 LTS _Lucid Lynx_ - Release i386 (20100816.1)/dists/lucid/main/binary-i386/Packages.gz Please use apt-cdrom to make this CD-ROM recognized by APT. apt-get update cannot be used to add new CD-ROMs
Failed to fetch cdrom://Ubuntu 10.04.1 LTS _Lucid Lynx_ - Release i386 (20100816.1)/dists/lucid/restricted/binary-i386/Packages.gz Please use apt-cdrom to make this CD-ROM recognized by APT. apt-get update cannot be used to add new CD-ROMs
Some index files failed to download, they have been ignored, or old ones used instead.)

2-when i install a new browser it always crash.................... (Why ubuntu keep doing this to me !!? ).