This could happen due to various reasons like :
1. Any recent update done.
2) Virus infected
3) Windows missing/corrupted files.
There are several steps to resolve the issue.
Try one after another and check if that fixes the issue.
Try this Fix
Click on the Download link and install the Fix No. 195 ( Restore Desktop Icons and Taskbar )Download Link
Press CTRL-ALT-DEL to bring Task Manager.
Click on New Task and type appwiz.cpl and click OK
This will re-run
Remove/Uninstall all new program you installed
before having this problem, Also remove the Windows XP Hotfix
Restart your PC.
The access to the
taskbar , icons will all come back and Install a new Antivirus.
If None of the above steps work, try a System Restore to previous date
Click START - All Programs - ACCSESSORIES - System Tool - System Restore
Choose the date before the system started giving trouble. ( The Date will be in bold ( highlighted ) which indicates the system can be restored to that date with all the settings on that date )*Note : Doing system restore will uninstall any software/program you have installed from the date you choose the system restore till current date, However it will not delete any files created )
Hope this is helpful.