Lightroom :: Catalog Has Disappeared From Left Hand Panel Of Library Tab

I am currently working with a trial version of Lightroom 4.2 and i have been doing some silly things. The end result is that Catalog has disappeared from the left hand panel of the library tab ie i only see Folders,  Collections and Publish Services.. 
 
I have tried to use File/New Catalog, Open Catalog and Open Recent but, in each case,  I get an error box appearing: " ....catalog address refers to a location that is not available" it does not close and re-open LR
 
Now for the confession as to how this situation arose. I had been using LR quite happily using the catalogue which was automatically created when i started. Then I decided to try creating a new catalogue, in fact I ended up creating a few new catalogues. I decided to remove all the catalogues and start again with one catalogue which I would set up (I was not worried about losing the updates to the photos  i had been playing around with) But, as i could find nothing within LR about deleting catalogues, I decided to remove them via Windows Explorer. When i went back into LR,  Catalog was still showing in the left hand panel  and, when i looked in Explorer, it was in the original folder My Pictures/Lightroom which I thought i had deleted along with all the other catalogues. Presumably it had been re-created automatically as in my original use of LR
 
I then compounded my mistakes by clicking on the + to the right of Catalog and, for interest, choosing whatever was at the top of the resultant list. It was at this point that Catalog disappeared never to be seen again.