If the software updates do not work, which is an excellent idea, here's a few other things to try.
Quit Safari from the Safari menu, or do CMD + Q while it's focused.
Make sure your computer has the correct date and time. Click it in the upper right and select Open Date and Time Preferences.
Click the Safari menu in the upper left, and choose Reset Safari. Make sure to uncheck everything, except "remove all website data". (You can optionally check other stuff if you like.)
Trash com.apple.safari.savedstate located in ~/Library/Saved Application State.
This might be worth a look, too: http://support.apple.com/kb/TS3230