Defragging D:\ drive makes it 'disappear'

[Guest Frances]

I have an Advent T9202 computer (XP home) with two 200GB hard drives. I can

defrag the C:\ drive ok but when I try to defrag the D:\ drive it becomes

invisible in Windows Eplorer. I had to use System Restore to make it appear

again.

 

Does anyone have any suggestions as to what is going on here?

Many thanks!