I am hoping someone can help me with this.

My laptop was working just fine with or without the power cord.

Then one day when I booted up without the powercord my display is so dim it might as well be no display. Reboot WITH the powercord and all is well. I can even unplug the powercord as soon as it has desktop and it still works ok - even for a number of hours.

Then one day when I booted up WITH the powercord my display is so dim it might as well be NO Display. So now - No display, WITH or without the powercord.

I can connect an external monitor and all is good on the monitor but not the laptop display.

BUT - If I close the lid far enough to energize the "LID IS CLOSED" switch then open it right back up, the display comes on in full brightness.....for about 2 seconds, then disappears again.

Any ideas ??? and it is NOT the battery.

There is a little microswitch that controls the on/off for the display. Typically when I hear of these issues I have people take a toothpick and clean THOROUGHLY the area around the switch. Look closely.

My old Toshiba would have this issue quite often. The power management utility that dims the screen to save battery power would get stuck in that mode. I would have to go in and switch it back to the full power mode, or use the Function hotkey to boost the brightess back up. Most laptops are going to have some icon in the systray that take you directly to power management options.

It is not a switch issue to turn the display off, because if I turn off all the lights I can still see the dim screen.

Others have said "power management".
I checked it out and there is nothing set for dimming the screen.
BUT - if I try to save any of the settings as default or Laptop, it gives "Error - two different versions....." something. Just going from memory.
I can save it to a new name, but doesn't help my display.

The key is shutting the lid triggers the switch and then it comes on bright........for 2 sec.

So I would agree it is the power settings but can't figure out what to do to fix it.

Thanks for the feedback.
I will keep trying.

Have you looked in your BIOS settings.

I have a Dell Latitude and the display settings are in BIOS with separate setting for running on battery or AC.

Most LCD in Monitors or laptops has a inverter that controls that, sounds like you have one that has a loose connection or is electronically having problems.

it may be the lamp

https://www.lcdparts.net/CCFL.aspx

Just to follow up with this.
With only a min this week and that week, it takes a while to get fixed.

But, everything I have been able to narrow down to is the inverter for the display is bad.
I guess it is "somewhat" common.

Now I just have to get it in somewhere to get fixed. If I wait for me to have time to fix it, it will never get done.

Thanks for the feedback.