First of all open your pen drive and goto tools in the menu bar.Now goto Folders Option and then press View tag.In that you will see a list of Cheakboxes for various tasks.Press Radio Button for Show Hidden Files and Folders and Uncheak "Hide Protected Operating Sytem file(Recommended).Now Press Apply and then Ok...
Now You would be able to see your files .....To make them clearly visible..Press Ctrl+A in your flash drive and then uncheak Hidden from the properties...ANd press Apply then Ok.
If inspite all the above solutions you are not able to see them.....JUST Install an Antivirus on your PC(if possible)
otherwise to copy all contents of pendrive to recover the data.DO the following:
1.Open start Menu
4.A command promt will flash.
[Drive name]: and press enter
for example if your pendrive is Showing drive G:
Then type c:\Documents and Settings\desktop>G: and press enter
Now type xcopy/s * [destination drive] and press enter key
g:\>Xcopy/s * c:\
6.And all your data will be recovered to c: drive