You need to go to the Yahoo program folder under your Program files folder. Usually, it is under you C: drive (where C is your computer hard drive).

Start >
My Computer >
Double click on C: >
Double Click on Program Files >
Find 'Yahoo' >
Open 'Yahoo' folder by double clicking >
Look for the Yahoo.exe file - this is usually seen as the yahoo icon >
RIGHT CLICK on that icon (yahoo.exe) file >
context menu will pop-up >
select |Send to| >
A sub-context menu will slide out >
Choose |Desktop (create shortcut)|
Close down all the windows.
Look at your desktop.
The Yahoo Icon will be there again.

[If you feel that the icons were recently deleted and may still be in your Recycle Bin:

Double click on your Recycle Bin >
Find the 'Yahoo' icon in the list of files >
Choose the file - it will show a as highlighted grey >
On the left find |Recycle Bin Tasks|
Under that you will find |restore this item| >
Click that >
Close down the window >
You should have the Yahoo icon back on your desktop> ]

Hope this helps