VOSTRO 1700 - Display only works on Battery power, black screen on AC

HI,
New to forums today.
My sister gave me a Vostro 1700 in Perfect condition. The PC works fine on battery power but when I plug the power in the display turns black in a few minutes. The laptop seems like it is running but the screen is dead. It is fine once the battery is charged and I can use it until the batt is dead. The battery is fine and I also tried another power supply.
I also was in setup and it does the same thing once the power supply is pluged in I do not have a display.
I hope this is a easy fix
THANKS SO MUCH

 

I would try;

- Test your AC adapter with a multimeter
- Use a known good Dell 90 watt AC adapter
- Remove the battery and AC adapter and hold down the power button for 30 seconds 2-3 times
- Use a known good battery

If you do all that and it is still shutting down, you have a short circuit on the motherboard somewhere.

 

I connected an external monitor and when the laptop's screen goes black the external monitor stays on. This is very weird, it is my sisters PC and she gave it to me because it just started doing this. I wish I could figure out how to fix it.
All the power supplies are good.
ANY SUGGESTIONS>>

 

OK - I was looking at the laptop's screen when it is dark and it is on put I can barely make out anything. It is like the brightness is at 1% if that makes any sense. The laptops screen just turns black after the AC is on for about 1 to 2 minutes. It will not power the LCD when the AC is on and the battery is out.
THANKS AGAIN

 

I have tried a new AC Adapter and same thing. I can ONLY use the laptop on Battery power. Once it is plugged in the display will go dark after maybe 1 minute. The external monitor will work on both battery and AC power. Which is not helping because I want this PC to be a laptop.
Could it be my OS?
THANKS

 

You can only troubleshoot when you start replacing parts.

Does your Vostro 1700 have the Nvidia graphics? It is a removable module. You would need to replace at least 2-3 of the following to troubleshoot (your LCD panel, your video card, your motherboard, your inverter/LVDS cable). There could be a possible short circuit in any of those. Unless you start replacing parts with known good parts, it is impossible to completely rule out anything.