Moved catalog to new computer but no longer recognizes my external hard drive. HELP!

My husband bought me a new MacBook Pro for my photography editing.  As exciting as it was, that has now faded with the large task of moving my LrC catalog to a new computer.  Firstly, for some reason LrC had updated catalogs over the years so I had about 4 diffferent catalogs that I had to merged.  Then, I finally got the catalog to my new computer.  However, now when I pull up my external hard drive to edit images, LrC says No file found. In fact, there are no folders underneath my external hard drive in LrC when I click to import.  In Library mode, I see my files, however it states The file is not found.  I have had this happen before when I moved files, and I clicked on the ? and helped Lr find the file.  However in Library mode, there is no ?. I think that if I can show Lr where the files are, it will resolve this problem, however I do not know how to do that when there is no icon to click.  Also, the pictures are blank.  My ratings are on each image, however I do not see the image itself.  Please help! This is impairing my ability to complete my job as a photographer and incredibly frustrating!!  Thank you!