Explorer EXE - Entry Point Not Found

I downloaded Service Pack 2 on my computer which uses Windows XP: Media
Center Edition 2004. The computer prompted me to reboot to allow the update
to complete, I denied it a few times but I left the computer and the update
restarted my computer. Only it took 5 minutes to get to my desktop and when I
did I got a message saying the following:

Explorer EXE - Entry Point Not Found
The procedure entry point SHCreateThreadRef could not be not be located in
dynamic link library SHLWAPI.dll.

It only displays my desktop background and nothing else, no icons or
anything. I can access Windows Task Manager.

Can anyone help me fix this?
Thanks in advance!