Cannot connect to a projector

I'm trying to help a user with a Dell Inspiron 1520 laptop that came loaded
with Vista. The graphics chip is the Mobile Intel 965 Express Chipset. She
was able to connect her laptop to a projector in her classroom until a couple
of weeks ago. Now it will connect, but only for a minute, then it switches
back to just being visible on the laptop. Hitting Function + F8, going to
the mobility Center, and changing display properties via the graphics adapter
makes no difference. Vista still thinks it is connected to the projector, as
I have it set now to change the wallpaper when in presentation mode in the
mobility center.

Here's what I have to do to make it work, even if only briefly:
- go to the Mobility Center, click "connect display" and make sure the "I am
currently giving a presentation" box is checked
- This causes the display to switch to 800 x 600, and nothing shows on the
external display. I then go into the display driver properties, where it is
already set to dual view and clone. I set the screen resolution to 1024 x
768, and click apply.

This allows the display to show on the projector briefly, from 1 minute to
almost 4 minutes one time. Then it flickers, and clicks off of the projector
display. The laptop's screen still shows the background I have selected for
when the display is in presentation mode, and Mobility center still thinks
it is connected.

I have checked power settings, different projectors (three different ones
show the same thing, and the projectors are from different manufacturers and
different ages.) I even tried a system restore to back before the laptop
started behaving this way, with no luck.

Anyone have any ideas? I'm all out :-(

Thanks very much!

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