Khalid, if it's just the data on your external drive, that will rule out everything as the cause, except for HDD failure, or corrupt data. If you remove the drive (optemized or not), whilst data is being accessed, your data
will become corrupt. When removing your HDD, make sure the HDD light has stopped flashing, and use the "Safely Remove Hardware" icon in the system tray. Also, make sure you take regular backups of your important data.
Khalid, the recovery of a corrupt drive, completely depends on how desperate you are to retrieve your data, how much time you have and how much you can afford. The best software product I've found is called R-Studio (
Disk Recovery Software and Hard Drive Recovery tool for Windows). Alternatively, you can send your HDD off to a data recovery specialist (
Removable Media Data Recovery - Intellirecovery.com). You may be able to find cheaper. Data recovery companies generally charge a little bit more, take a little longer to return, however the recovery rate is normally much better.
EDIT: Marked as Answered.