Several things to try ...
From your Safari menu bar click Safari / Preferences then select the Security tab. Deselect: Enable plug ins Quit then relaunch Safari. If Safari loads pages, troubleshooting help here. Unsupported third-party add-ons may cause Safari to unexpectedly quit or have performance issues
Check Safari / Preferences - Extensions. If you have any installed, turn that off, quit, relaunch Safari to test.
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.
Try troubleshooting the Safari .plist file (preferences).
Go to ~/Library/Preferences
Move the com.apple.Safari.plist file from the Preferences folder to the Desktop.
Quit, relaunch Safari to test.
If that helped, move the .plist file to the Trash, If not, just move it back to the Preferences folder.
Try Safari in another user account. If Safari won't load pages there also, then it's possible the startup disk needs repairing.
Use Lion Recovery for that.
Im having the same problem in firefox, and it JUST started. My macbok pro is about two months old and Ive had zero issues until now. Until two days ago I was able to visit any site, including mine that I cant access now.
And its only certain website.. in my case its the domain I own. So I cant ftp in even to upload files, I cant view the site or anything.
If you google the issue, lots of folks are having it, but have not found a anyone who has posted any fix that worked.
Most are of the opinion it's a dns issue... but the open dns suggestions havent worked.
Since a couple of weeks I am having exactly the same problems w. Safari. Firefox on the other hand works perfectly fine... I'm on a 17" MacBook Pro w. 10.7.4 Have tried to 'reset Safari', and had conversations w. Apple support. Just had a call w. my ISP for the possible DNS issues, but they could not help w. nothing... I'm using Safari from when it was introduced - Something must have gone fundamentaly wrong... Jan
The following has been used successfully by several people with various Mac OSs when other remedies have failed. Use the following if Safari fails to function correctly in only one account. This will delete all Safari items in the problem account. All Safari preferences will have to be reset:
1 - Log into the problem account
2 - Export Safari bookmarks
3 - Quit Safari
4 - Open Terminal - in Utilities
6 - Paste the following into Terminal and make sure it is complete especially first and last characters
mv ~/Library/Safari ~/Desktop/Safari-`date +%Y%m%d%H%M%S`; \
rm -Rf ~/Library/Caches/Apple\ -\ Safari\ -\ Safari\ Extensions\ Gallery; \
rm -Rf ~/Library/Caches/Metadata/Safari; \
rm -Rf ~/Library/Caches/com.apple.Safari; \
rm -Rf ~/Library/Caches/com.apple.WebKit.PluginProcess; \
rm -Rf ~/Library/Cookies; \
rm -Rf ~/Library/Preferences/Apple\ -\ Safari\ -\ Safari\ Extensions\ Gallery; \
rm -Rf ~/Library/Preferences/com.apple.Safari.LSSharedFileList.plist; \
rm -Rf ~/Library/Preferences/com.apple.Safari.RSS.plist; \
rm -Rf ~/Library/Preferences/com.apple.Safari.plist; \
rm -Rf ~/Library/Preferences/com.apple.WebFoundation.plist; \
rm -Rf ~/Library/Preferences/com.apple.WebKit.PluginHost.plist; \
rm -Rf ~/Library/Preferences/com.apple.WebKit.PluginProcess.plist; \
rm -Rf ~/Library/PubSub/Database; \
rm -Rf ~/Library/Saved\ Application\ State/com.apple.Safari.savedState
7 - Hit return to execute the above
8 - Start Safari
9 - Test Safari
10 - Reset Safari Preferences
11 - Click Reset on Safari menu and and adjust as required for future resets
12 - Import bookmarks