This question already has an answer here:
My terminal emulator shows the following error while trying to install Dropbox. I need help and I am a beginner in Ubuntu.
Reading package lists... Done Building dependency tree Reading state information... Done Some packages could not be installed. This may mean that you have requested an impossible situation or if you are using the unstable distribution that some required packages have not yet been created or been moved out of Incoming. The following information may help to resolve the situation: The following packages have unmet dependencies: nautilus-dropbox : Depends: dropbox but it is not going to be installed E: Unable to correct problems, you have held broken packages.