E510 Goes Black When Desktop Comes Up

I have a Dell E510 that has been running Windows 7 Ultimate fine for a
while. I put it on the shelf in October 2015, and brought it back out
last night. I forgot the password, so I used the Dell supplied OS
disk, went into repair, and used the sethc.exe method to reset the
password:

http://www.howtogeek.com/96630/how-t...otten-windows-
password-the-easy-way/

This worked, but now the monitor power light goes from green to orange
(power saving mode), the keyboard lights go out, and the mouse light
goes out. I can hear the power supply fan still going. Thinking it may
have been a problem with the discrete video card, I removed it and set
to use the onboard video. Same problem. The problem also exists in all
Safe Modes.

Funny, though, as long as I don't enter my new password, the thing stays
on. That is, it will sit there forever asking me to enter my password,
but as soon as I do, everything goes out either immediately after
hitting Enter, or a few seconds after the desktop comes up. I've tried
a different monitor, too, but same problem.

Any ideas?

TIA