You can try resetting the icon cache by making a change to the cache and then changing it back. Here's how:
1. Right click an empty area of your Desktop
2. Select Properties
3. Select the Appearance tab
4. Choose the Advanced button
5. In the "Item:" drop down menu, click the entry titled 'Icon'
6. Using the up or down arrows, change the number displayed
7. Click OK
8. Using the above instructions, change the value of step #6 back to its original position.