Opening Winfdows login screen goes black

[Richard Jost]

When I turn on the computer and monitor, the computer
boots up fine and I see the first screen of the Windows XP
login screen with the green activity bar. After a few
seconds, that screen disappears and the screen reverts to
black, even though it sounds like the computer is booting
up. Since I can't see the screen, I don't know how to
proceed! Any suggestions on what may be happening?

Thanks for your assistance.