Without proper system info such as what Mac and what version of OSX nobody can say much and the logs from your Log Viewer would also help. Well, whatever. As a start run teh cleaner tool and reinstal lthe software.
Hey! I tried this and it still didn't work. I don't know what is wrong with it. I have the Web Premium CS 5.5. I uninstalled did the cleaner restarted, installed again and photoshop still doesn't open.