The limited amount of information that you provide here is not enough to understand
what you are doing or what is happening. Please be more detailed in your explanation. Specifically, the following questions should be answered:

1. What is it that you are referring to as "Project Explorer"? Describe
   what it looks like in as much detail as possible.
2. What do you mean by "disappearing immediately by help of an Add-on Disc file"? Describe the steps you take prior to this happening and how it happens in as much detail as possible.
3. Can you make it reappear by selecting View:Project Explorer when Origin 6.0 is running? Or is the "Project Explorer" that you are referring to not the same as the one you see when you select this menu?
4. Does the problem happen when you install Origin 6.0 and select the check box next to "Yes, I wish to install AddOn disk now"? If yes, what AddOn are you attempting to install and at what point during the installation does "Project Explorer" disappear? If not, when does it happen?

Again, please be as detailed as possible so I can try to reproduce the problem.

Sincerely,
Ryan Toomey
Microcal Software, Inc.