external hard drive

Asking here, because I don't know where else to ask. My external hard drive was taking a while to load, like it usually does. Meanwhile, I was joining a forum, and wanted to upload a picture for my avatar. When I tried, however, my browser froze with the spinning rainbow swirly. So, I figured I'd let it do its thing while I searched in finder for the image, just so I could easily find it when the internet unfroze. My external hard drive still hadn't loaded, and by this point it had been much longer than usual. I decided to eject it, but then finder froze as it was ejecting.

I couldn't do anything the top toolbar even to make finder relaunch, so I tried to shut my laptop down. It wouldn't shut down when I hit "shut down", so I waited a bit, and then pressed the button again. I then got a message saying, "Your computer is already shutting down". So I waited a little longer, and then it said that Chrome wouldn't respond and would I like to force quit? So I did. My laptop still wouldn't shut down, so I pressed the button again and just held it till the laptop turned off. It immediately came back on again and I opened Chrome while the desktop was loading, only to discover that the desktop wouldn't load at all and my external hard drive was making clicking noises. Then I got a message saying something like "Cannot repair disk, you can copy and open existing files, but you cannot save. Back up files and reformat as soon as possible".

Since my desktop wasn't loading, I closed Chrome and shut the laptop down again and then unplugged the external drive and left it for about five minutes. I turned the laptop on again, and the desktop loaded like it should. I opened finder and that was fine. I then plugged in the external hard drive again, but then I got that message again. I went to Utilities and opened Disk Utility, but when it opened it just froze with the spinning rainbow swirly. So I force quit that and tried to look up what my problem could be but didn't find what I need, and then I opened Disk Utility again, and this time it showed my disk. But when I clicked on it it froze again.

So, I would like to know what I'm supposed to do here? It's a seagate external hard drive, and I'm on a mac book pro OS X 10.9.5. I really hope I haven't done something to permanently damage my external, and if I have, I'd like to know if and how I can retrieve my files. Thanks!