This can also be a network card driver error. Check for the latest vista drivers for your NIC - and confirm it is supported by Microsoft for Vista.

I had a similar problem at start-up that sent the whole screen black - although I could still ctrl-alt-delete. Turned out it was the DHCP service failing to start due to an incompatibility with the TCP/IP driver. Only got the screen back when the service had restarted - default wait of 2 minutes dependent upon the value in the recovery DHCP Service property page. Minimum you can change it to is 1 minute!

If you look at the dependencies for the DHCP service and you see NETIO Legacy TDI Support Driver that is most likely your problem.

Even if not it's always worth trying a different NIC. Microsoft do need to fix this though and at least give some feedback to the user.