Desktop and taskbar items disappear.

I am running a network with NT4 SP6. This time while closing out the internet options, it stopped responding. The items on the desktop and task bar disappeared. I can open the task monitor and start or open an item from there but then the box will not close. The network appears to be running ok, I have about 40 users with no complaints. The control-alt-delete allows me to sign off or back on but until I can reboot the icons are still missing. This is the second time this has happened to me in the last couple of months. When I reboot the server it appears to solve the problem. Is there an underlying problem that is causing this or does anyone know why this happens. All help is appreciated.