my pen drive or sd card opens but doesn't show the data inside it.

1. if your pen drive or sd card open and not shown data then you can do the following to 
Make sure all files and folder are not hidden in your pen drive or sd card. to do this do the following. Check if the files are not in hidden mode 

Click on "Start" -->Run --> Type cmd and press Enter. 
Here I assume your pendrive drive letter as G: 

Enter this command. 
c:>dir/ah   ( to see all hidden files)
C:>attrib -h -r -s /s /d g:\*.* --> Press Enter (to unhide all files)


You can copy the above command --> Right-click in the Command Prompt and 
 and check your files.

2. Second Method :
-  Insert your SD Card or Pendrive in to system
- copy the address
- open the chrome and pest the address in url bar
- now your good to go
- click and hold the file you want to recover and drag it into the location you want to recover.
- Now you can recover your files