I agree with trekzone, sounds like something is wrong with the drive. Get a drive diagnostic utility like SeaTools and check the drive. No sense trying to defrag the drive if it is operating so poorly it can't be used. In fact, if you can't use it now, the drive is probably hosed.
Try the drive on a different computer just to rule out any odd USB issues.
In case you just learned how to click on things and you know what a computer is, not being mean, but these answers can be overwhelming. Google is your friend. Search for "how to use seatools" or "how to use defragger". If you are having further issues, let us know. Also would be good to know how much you know about computers, and if there is someone there that might understand a bit more about what we are talking about, that would be a plus.