I think I've denied myself access!

Hello
I've been attempting to get the Membership plug in up and running but I think I may have denied myself access!

I am (obviously) the Wordpress site Administrator.
I seem to have done something that results in the following -

When I Activate the Membership Plug In -

1) I no longer get the Membership item in my vertical Wordpress window on the left.

2) I no longer get the SITE ADMIN option on my Wordpress pages (though I can navigate there by clicking on "EDIT" on a post or page).

3) When I use the WPMU plug in manager and I click on CONFIGURE for the Membership plug in it tells me I don't have privileges.

4) I don't get a DELETE option on the WPMU plug in manager page.

I suspect all this points to having somehow denied myself access - but I don't know how I did it, and more importantly I don't know how to put it right.

Fortunately I am able to Deactivate the Membership plug in, but I was just getting to grips with it and I'd like to see if it does what I need.

Help anyone?
Thanks
D