This one is really easy - miss having the administrator on the Welcome screen? You can really easily put it back on there with a command from Run.

1. Go to Start, and in the Search box type in cmd.
2. Right click the Command Prompt at the top of the Start menu and select “Run as administrator”.
3. At the command prompt, type in net user administrator /active:yes then press Enter.
4. Log off and you should see the administrator sitting there on your Welcome login screen.

Source: VistaBase