How do I open a second instance of digital editions?

I thought I had backed up my book files from my old computer, but what I backed  up wasn't.   I copied the book files from my Kobo ereader to the new computer, but some very fast passing messages seemed to indicate that some books were not copied.   I thought to open a second instance of ADE, so that I could compare the files on the Kobo to the files that got copied to the computer, but cannot figure out how to open a second instance of ADE.    The Kobo ereader is updated to current.   The PC is using Win7 updated to current.  ADE is current.