Black screen only

It appears to be the issue with the ram. Turn off laptop, remove battery and unscrew the the cover to the RAM. Its on the back panel. Remove and reseat the RAM after cleaning the gold pins.

You can also use the Microsoft memory diagnostic tool.

the motherboard could have gone bad. try to remove the battery and turn on the computer using only the ac adapter.

Sounds like a failure of the LCD backlight. This will require replacement of the inverter or the LCD itself:
http://support.dell.com/support/edocs/systems/Latc640/sm_en/display.htm#1001077
You can buy parts here:
http://shop.ebay.com/?_from=R40&_trksid=p3907.m38.l1313&_nkw=C640+LCD&_sacat=See-All-Categories

I suggest you DONT USE PINCH POWER CORD FOR SAFETY.

PLEASE TELL ME IS YOUR POWER CORD & THE PINCHED CORD ARE SAME? I MEAN SAME MODEL? AFTER PLUGING OF YOUR CORD, THE BATTERY CHARGING LIGHTS ITS ON? IF NO THEN I GUESS THAT CABLE NOT SUPPORT HER LAPTOP.
VISIT A DELL SERVICE CENTER OR A SHOWROOM AND BUY NEW CORD WHICH IS MADE FOR YOUR DAUGHTER LAPTOP MODEL.
OTHER WISE SOME CHANCES OF SHORTCIRCUIT ON MOTHERBOARD.

Thanks, i am waiting for your feed back & if you satisfied then thumps me please.

hello ! I don't think so coz there made different and diferent connections .

And if not carefull u will end up burning that screen
S i suggest that u get a new cpx screen and fix it

good luck dude

Plug the adaptor into the wall and the other end in to the laptop

check power supply see if its putting out voltage to laptop

Try putting the computer into safe mode by holding down on the F8 button and selecting safe mode during the boot process. Once you get to the safe mode screen and windows appears, restart the computer.

If that doesn't fix the problem you will have to restore Windows.

Symptoms of a Bad Video Driver

Monitor Resolution issues: screen flickers, screen is cloudy, screen shows horizontal lines, screen goes black, goes blank, goes into sleep mode, goes into power mode, size magnifies or reduces, video is jittery, fonts change, screensaver will not appear, cannot extend display on dual monitors.

Download it from here
VIDEO DRIVER FOR LATITUDE

check the video cable and see if it;s properly seated. run the laptop with something that uses memory. if the video chip it going to show signs of problems, it will be more prominent when the laptop gets hot. most cases laptop motherboards have integrated video cards and cannot be replaced.