Thunderbolt / firewire adapter issues.

I was excited to get the new IMAC this past December. In doing so I expected my 4tb caldigit external drive to work with the adapter I purchased. When I first hooked it up and turned on the drive it seemed to be having a hard time locating the computer. Finally it would find it and work. However, now it's not even finding it and I'm not sure what to do. The drive goes into a please wait mode and just sits. I have some very important media files on this drive and I don't know how to fix this.