Removable disk contents are not visible

Question

I found ur site is very useful.Can you throw a light on the problem which I found in my Pen Drive.Pen drive shows 700 MB used memory space & 270 MB free.But I am not able see or find out the contents in the Pendrive.Also I am able to copy in the pen drive but after copying if I do "Refresh" the data becomes invisible & unable to get located even using search.How can I extract my data & why this problem is arriving?Kindly provide the solution on [e-mail]