According to the message on the screen.
"To use the Assets panel, you must define a site"
Thankyou Mr, john I'm hyo r, jeon I was purchase dream weaver cs5.5.. I use it is few days ago the assets panel is normal ... now I work design when insert image. the assets panel display same images automatic . but now dosn't. it is my question... thankyou.
Open Dreamweaver. On the top menu bar, go to Site > New Site > Define your site (at least locally). Load your site files into this site within Dreamweaver. The Assets panel will definitely work once you accomplish this.
This video tutorial should help you: http://tv.adobe.com/watch/learn-dreamweaver-cs5/gs01-defining-a-new-si te/