I recently configured my wireless adapter (WG111 NETGEAR) and after restarting my computer i realized my login screen and a couple of other user options were disabled, all that was available was a plain old black background with a dialog for login. Anyway after receiving a detailed email from NET GEAR support i discovered it was only a key in the registry that was messing it up
Here are the instructions i took to resolving this problem:
1) Delete the key
GINAdll from the following registry path (in registry editor)
HKEY_LOCAL_MACHINE/Software/Microsoft/Windows NT/Current Version/winlogon
2) After deleting it go to the
Control panel --->
User Accounts --->
Change the way users log on or off
and make sure the welcome screen and fast user switching are both checked
That is all there was