MacBook and External NAS - Folder Cycles Through Files

I have a MacBook and a Western Digital NAS. I just moved over several GB of files to it and now when i go to open the folder it cycles through all the files then the screen goes blank and all folders disappear and the desktop appears. When it does cycle through the folder if i try to move through the folder or change how the folder is sorted it goes to the beach ball and spins, spins and spins (during this time the computer gets loud as if the fan is spinning). Any ideas what the problem is.