You have to re build the icon cache database. Just follow this instruction step by step. You can take a print out of the page if you are not sure what are you going to do.
1. Close all folder windows that are currently open.
2. Launch Task Manager using the CTRL+SHIFT+ESC key sequence, or by running taskmgr.exe:
3. In the Process tab, right-click on the Explorer.exe process and select End Process (See the screenshot).
4. Click the End process button when asked for confirmation.
5. From the File menu of Task Manager, select New Task (Run…):
6. Type CMD.EXE, and click OK:
7. In the Command Prompt window, type the commands one by one and press ENTER after each command:
CD /d %userprofile%\AppData\Local
DEL IconCache.db \a
Note: %userprofile% represents the path to user profile folder.
8. In Task Manager, click File, select New Task (Run…)
9. Type EXPLORER.EXE, and click OK: