How can I convert (expand) all parts of my design in objects?

I've tried 'object to path', but that didn't do the job

I think you want "Break apart". I think it's in the path menu (sorry, I don't have Inkscape handy to check).

Yes, Break Apart is in the Path menu, as microUgly said.

Mikeymike wrote:How can I convert (expand) all parts of my design in objects

But I'm not at all clear what you mean. Do you mean that you're using a pattern fill, and it needs to be bigger? (expand in objects)
Or maybe you mean 'convert to objects'? "Objects" can be kind of a confusing term. If not Break Apart, then Ungroup might be the trick.

If none of this helps, maybe you could clarify. Screenshots can be very helpful, if you can do it