In 1 of my assemblies, I have 1 part that I cannot edit. When I right click, it only has OPEN, CLOSE, DELETE ETC. But no edit. 

I knwo where there are online demos for Inventor every week, you can see the topics coming up at www.quadrasol.co.uk then go to the Autodesk section, into whats on and then webinars.  The next one is tips and tricks I think.

HiI have found this happens when I have the file already open, maybe minimised.