Switch User Function Turned Off in Windows Vista Home Edition

I have multiple users on my home computer, but Windows Vista will not allow us the "switch users" option anymore.   For a couple of weeks I worked from home, and my IT guys had me install a couple of software packages including a VNC software, all of which I later uninstalled.   From then on, I had no "switch user" option.   I tried finding an older restore point, but there wasn't one listed from before that time.   I'm guessing a registry setting was changed that the uninstalls did not fix.  Can someone help me turn the "switch user" function back on?