Please go to : C:\Users\(User_name)\AppData\Roaming\Adobe\
Find and Rename the Adobe Photoshop CS3 Folder to Adobe Photoshop CS3_old
Find and Rename the Photoshop Folder to Photoshop_old
Rename the folder will create a backup of Photoshop prefrences. Then try to launch the software again (it will create the prefrences of the software again).
Appdata is a Hidden folder
Please go to My Computer, On top left hand side you will find Organize click on Organize, Click on Folder and search option.
You will get the Folder Options window on the screen. Click on View tab and Select "Show Hidden Files, Folders and Drives" then Click Apply and OK.
then try to search the AppData.