i was copying some files to my external USB HD and my mac froze, the colorful round ball was spinning and spining, so i turned of my PB through the turn off button. It restart well, and everything works, though when i plug my HD back in it doesnt recognize it, i tried turning it off, restarting my mac, and all the possible solutions, nothing works. Can someone please tell me how to fix this because i have some important stuff on there. Thanks.

*Update* Now the HD shows but it works VERY VERY slowly. I wonder if it is the HD or my system. My mac works perfectly fine everywhere else, though when i try to copy from the external HD everything is incresible slow. instead of 15 minutes it will take like 3 hours to copy something. Though when i copy To my external HD the speed is normal.