Have you gone to Edit > WebAssist Preferences and made sure that Disable Preview isn't checked?
If that's not the problem, post your build numbers and what platform you're on and a tech support engineer will help you.
Your friends over here at WebAssist! These Dreamweaver extensions will assist you in building unlimited, custom websites.
These out-of-the-box solutions provide you proven, tested applications that can be up and running now. Build a store, a gallery, or a web-based email solution.