WIn98, Ctrl+Alt+Del does nothing

A client with a Windows 98 laptop is trying to run defrag and it keeps restarting. He gives it the 3-finger salute to see what is running, but nothing happens – no Close Program box, nothing.

My question is: Where do I look to fix the Ctr+Alt+Del problem so he can kill whatever is accessing the HD and let defrag run?

As a workaround: Where is the executable to bring up the Close Program dialog box?