Making a Master clip in FCP 7

Hi , I am trying to make a master clip ( rather than a subclip) from a sequence in my viwer which remains grey in my Viwer menu , the subclip is only avaible as black in the menu.

How do I acess the master clip .

I am working in PAL SD in FCP 7.

I know this is pretty basic but I cannot understand why I cannot acess the master clip from the viwer

Thanks

Dave