When DW starts acting weird, the first thing to try is Deleting Corrupted Cache in DW
http://forums.adobe.com/thread/494811
If that doesn't help, try Restore Preferences. Note: your work space, custom settings & 3rd party extensions will be wiped out by this. So make backups of anything you need to keep.
http://helpx.adobe.com/dreamweaver/kb/restore-preferences-dreamweaver-cs4-cs5.html
If all else fails, use the CS Cleaner Tools below followed by a software re-install.
http://helpx.adobe.com/creative-suite/kb/cs5-cleaner-tool-installation-problems.html
Good luck!
Nancy O.