When looking for information about people who have already died, you might want to use the keyword 'obituary' in your searches; especially if you're not having a lot of luck finding formal biographies.
Because this information is usually printed in newspapers, you might try ProQuest Newsstand, for best results. In fact, this database even lets you limit your results to obituaries!
Each of the following databases contains biographical information, although some will have more than others.
A great place to start is with Credo Reference, which is a collection of online encyclopedias where you might find multiple biographies for the person you're researching.
You may also find biographical information in other databases, but they may be subject-specific (Oxford Music Online, etc.).
If you're not having luck with one database, try others and compare your results for a more complete picture of the person you're researching!
It may be especially difficult to find biographies on some people.
In these cases, you might consider searching for articles about them, instead of strictly looking for biographies. Sometimes you can piece together a complete picture by using bits and pieces from different sources.