Assembly is lost when using the mouse wheel to rotate.

Wayne Beede wrote:

Any suggestions would be great I do not want to rebuild it again.

Can you attach your assembly here and end all doubt?

Save Copy As a back-up.

Remove components one-by-one and test.

Does it suddenly work as expected with removal of a particular part?

Have any imported parts?

Any parts with Loft or other complex geometry that you had trouble modeling?

Tiny parts (out in space) compared to large assembly?

Pretty picture screen captures?

It looks like a component or an entity like sketch, origin, plane etc. has been placed far away from the assy origin and hence you are seeing this behavior.

Depending on your SW version, you can use Tools > Evaluate > Performance Evaluation (Formerly AssemblyXpert) to find out that component or the entity creating the issue.

If Performance Evaluation doesn't work out, then suppress all components and then start unsuppressing them one by one to find the culprit.

I assume that there is a problem with graphics capacity.  What is the capacity of your graphics ram?

I don't know if this is what you're looking for or not but if you middle mouse button (scroll wheel) click on a face or edge, then depress the same button and drag, the selected face or edge will become the center of rotation.

Try this:

https://www.symsolutions.com/symblog/item/my-solidworks-assembly-disappeared

Copy paste from website:

To reset your bounding box and hopefully be able to view your assembly, do the following:

• Move your cursor to the graphics area.
• Hit space to bring up the “View Palatte.”
• Double click “Isometric.”
• Type CTRL-Q.
• Then save the assembly.