My comp asks me to formet my hd

Hello,

i just bought a new external hd, i had finished backing up all the files i had on it. a few weeks later i tried to transfer some more stuff and it took me about 45mins to 1hr to transfer all the info on there i thought that was odd so i asked someone and they said to run defrag my hd and run error-check and have it auto-repair bad sectors.... took me almost the whole night to do it but when i woke up in the morning it seemed everything had finished. now everytime i plug my hd into any comp the auto-run doesnt work, then when i got to my comp... the icon shows up and when i click on it... my explorer stops responding for about 5-10mins and when it does kick back in it asks me to format my hd... i have some very important files saved on there and i cant afford to format it. can someone plz help me.