Did you try pinning from an open or closed program? With an open program, right-click the program's button on the taskbar to open the program’s Jump List, and then click Pin this program to taskbar. With a program that is not open, click Start, find the program’s icon, right-click the icon, and then click Pin to taskbar.
If it still doesn't work for you, Shawn's suggestion of a System Restore is worth a try.
Microsoft Windows Outreach