admin acct gone on Dell Latitude D630 laptop

Have run a clean up on Latitude 630 and now at start-up the Administrator account choice is gone. Any ideas on how to correct? Thanks.
thank you

Thank you for replying. Problem is that I no longer even get a screen with a taskbar and START button in lower right. Only see the default wallpaper, nothing else.
press crtl + alt + del all at once, may have to do it two or three times, this will bring up task manager, in task manager, go to file, new, and type in explorer.exe, this will bring up the task bar and desktop