You should update to Safari 5.0.3, but in the meatime:
If your Safari won't open, one or more of the following procedures should fix it:
1. Go to Home/Library/Safari/ folder and remove the following two files:
history.plist
lastsession.plist
(Safari may not load properly If these two files are corrupted.)
2. Go to Home/Library/Caches/Metadata/Safari/ and remove the
contents of that folder.
(These are just webhistory files and are not required for Safari to run. However, similar to preference files, problems can arise if they have become corrupt.)
3. Locate the cookies.plist file that's located in the Home/Library/Cookies/ folder and remove it.
(Again, faults in stored cookies may interfere with Safari's launch.)
4. Check whether any of your third-party internet plug-ins may be interfering with the launch of Safari by carefully moving them to the desktop (do NOT delete them at this stage). You can find these in two places:
Home/Library/Internet Plug-Ins/ folder, and Global plug-ins are located in the Macintosh HD/Library/Internet Plug-ins/ folder.
Also look in Library/Input Managers where other third party add-ons may lurk. If you find a SIMBL folder, please note that some SIMBLE.bundles may require updating or possibly removal. More information on third party add-ons here:
http://support.apple.com/kb/TS3230?viewlocale=en_US
Restart Safari and place them back in the correct folders, one at a time, closing and re-opening Safari each time. If you discover that one of them was causing the problem with launching Safari, trash it and download and install a fresh copy.
Note also that Safari does not accept any third party tool bars. If you have installed any of these, delete them, or post back for instructions on how to do so.
