How often has this happened to you? You're working on something at the server when a window locks up. Your only recourse is to open the Task Manager and kill the Explorer.exe process, which kills the offending window—as well as the desktop and taskbar. This can confuse system tray icons that won't function properly again until you reboot the system.
This occurs because of Windows Server 2003's attempt to be efficient with the Explorer.exe process, which is responsible for the desktop, windows, and more. The OS runs all of these as a single thread. But by separating the desktop and taskbar functions from the other windows, you can achieve fewer problems, even if it's not quite as efficient.
Follow these steps:
After the reboot, Windows Server 2003 will have two processes called Explorer.exe. One is responsible for the desktop and taskbar, while the other handles open windows.
Note: Editing the registry is risky, so be sure you have a verified backup before saving any changes.