|First of all, we see this "I have some very important data in it which i cant afford to loose" message almost daily.|
External drives are not meant to be your ONLY copy of important files. You should keep at least two copies of any files you need.
Now, go to Windows disk Management while the external is connected. Look there to see how it shows. If the file type is RAW this means the partition has been corrupted. Most likely by improperly removing the drive while it was still writing. You should always use the safely remove icon in the tray before disconnecting.
If your see the drive listed in Disk Management download a utility called testdisk, which shoudl be able to repair the corrupted partition. Be sure to read all tutorial information BEFORE using. If you are unsuccessful in repairing the partition then use recuva to recover the needed files. Get both at the links below.