Can't get Calibre to display library

I don't know if this has happened due to the last upgrade, but I am using Calibre to convert e-pubs and sending them direct to Kindle. The books I add from the Adobe Digital Editions come in okay and I convert them to Kindle and Send to Kindle okay.

However, I cannot get back to the Calibre Library... all that displays on opening is some of the recent epubs from ADE, but not all of them.

Is there a keyboard shortcut to display the Calibre Library?

Thanks,
Peter