I have a had a similar issue after swapping drives around and found that changing the drive letter to something that hasn't been used before worked. Also try checking the event viewer logs for anything that might indicate an issue with the drive, filing system etc.
To change the drive letter you need to right click my computer, choose manage and then choose disk management. Right click on the dirve (if it's there!) and choose change drive letters and paths. If that fails check in the event viewer again unders system management and see what it says in there - post back if you need to.