I've read your post several times and I'm afraid I still don't understand what the problem is. So your hinges were assemblies, and you saved them as parts? And now you can't open the part and edit it, or click on a part in the assembly and choose the "Edit component" icon? If you can clarify I'm sure someone can help you.
Like Glenn, I'm not quite sure what the problem is, but I'll take a shot at solving it and offer a bit of advice.
First, your reason for saving your hinge assembly as part in order to be able to scale it doesn't really make sense. By saving it as a part, you've lost all sorts of editing ability. However, the screen grab you show for the hinge shows it as an assembly, so I'm a bit confused what you did. If the hinge is to remain static in the upper level assembly, just create it as a single part. You can then easily edit your sketch so that the hinge will be properly sized for the overall assembly.
Second, as Glenn mentioned, you can edit a part in the context of an assembly. (I suspect you know this given the fact that it appears you have some parts that look like they were created within an assembly.) Position a hinge to where it needs to be, use your measure tool to figure out how far off locating feature are and edit them accordingly.
Hope some of this helps.