You have installed new software or you have tweaked preferences – it probably is giving you a problem. You can determine the problem by logging into your Mac as a different user. If no other account exists on your Mac, you can create one now.
If logging in as a different user resolves the problem, it means that the problem is not with the OS X rather the cause for the problem is a particular file in the user folder. It means that the problem can easily be fixed without doing something too much like reinstalling OS X or removing everything from the disk.
The cause for this problem is most probably a conflicting or corrupted file in the Library folder inside your user folder – it could be a font, preferences file, a plug-in or a cache file.
There are many utilities available for repairing corrupted files. For instance Leopard Cache Cleaner can be used to remove corrupt cache file, you can use Font Book’s Validate Font command to repair corrupt fonts. Find out corrupt .plist files with Preferential treatment software