Your configuration folder may have become corrupted. You can rename the configuration folder to have Dreamweaver recreate it. Close Dreamweaver and go to:
WinXP
-DW8
--C:\\Documents and Settings\\<Your User Name>\\Application Data\\Macromedia\\Dreamweaver 8
-DWCS3
--C:\\Documents and Settings\\<Your User Name>\\Application Data\\Adobe\\Dreamweaver 9
-DWCS4
--C:\\Documents and Settings\\<Your User Name>\\Application Data\\Adobe\\Dreamweaver CS4\\en_US
Win Vista
-DW8
--C:\\Users\\<Your User Name>\\AppData\\Roaming\\Macromedia\\Dreamweaver 8
-DWCS3