Shortcut icons on my desktop started showing up as a default icon (generic blank icon), but the programs still work fine. This might be caused when an Icon is a link to another Icon that links to the target file. The following steps worked to recreate the icons.
1. Browser the computer to the actual file location. Example: Excel 2007 is installed in c:\program files\Microsoft office\office12\excel.exe
2. Right-click the target file, “Excel.exe” and select "Send to", then select "Desktop (create shortcut)".
3. Click "Yes" when prompting with the warning to replace the old shortcut file.
The icon should appear correctly.
If the Icon is located on the Taskbar or the Start Menu it might be because of the same reason. Remove the icon, browse to the target file and click “Pin to Start Menu” or “Pin to Taskbar”. The icon should appear correctly.
Hope this helps!