HI Pierre ...
Several things to try ...
From your Safari menu bar click Safari > Empty Cache. Quit then relaunch Safari to test.
From the Safari menu bar click Safari / Reset Safari. Select the top 7 buttons then click Reset. Try Safari.
Check Safari / Preferences - Extensions. If you have any installed, turn that off, quit, relaunch Safari.
Quit Safari. Open a Finder window select your Home folder in the Sidebar on the left. Then open the Library folder, then the Caches folder, then the com.apple.Safari folder. Move the cache.db file from the com.apple.Safari folder to the Trash. Relaunch Safari.
From your Safari menu bar click Safari / Preferences then select the Security tab. Deselect: Enable plug ins Quit then relaunch Safari. If Safari speeds up loading pages, follow the troubleshooting help here. Unsupported third-party add-ons may cause Safari to unexpectedly quit or have performance issues
By the way... since you are running Lion v10.7.3, in order to reinstall apps such as Safari, you need to use Lion Recovery
edited by: cs