Unreadable disk error
I have been using a LaCie external hard drive as my Time Machine back up. Until today, it worked perfectly. Today, I tried to manually force a back up before I shut down my iMac. The spinning wheel wouldn't stop and nothing was happening. When I opened the force quit window it indicated that Finder was not responding. After I did a force quit and restart, I now get an error message that the disk I inserted is unreadable on this computer and do I want to initialize the disk. Does this mean I have lost all the back up material I had on the disk? Is there anyway to salvage it?
Using iMac running OS 10.8.5
LaCie 750gb external hd connected by USB