It is the screen Inverter, or the LCD screen itself.
Screen Inverter: A small circuit board located behind the Display Bezel, and mounted towards the bottom of the LCD screen,http://support.dell.com/support/edocs/systems/vosA860/en/sm/display.htm#wp1183775
The yellowish long object, at the bottom, is the screen Inverter.
Here is another look at it,http://www.batterycenturys.com/dell-vostro-a860-inverter-p-185294.html
Dell Support > Vostro a860 Notebook PC > Service Manual,http://support.dell.com/support/edocs/systems/vosA860/en/sm/index.htm
In the list clicking on -> Display, will get you to the first link above.
Need guidance in replacing the screen Inverter, post in a Comment.
(Just a basic guide using a Vostro 1014/1015 Notebook PC. Not yours, but good for basic guidance. This is replacing the LCD screen,
An LCD screen cannot produce light by itself,http://solutions.3m.com/wps/portal/3M/en_US/NA_Optical/Systems/BehindTheScenes/Optics101/
( Click on the small window with the monitor in it )
It needs an additional light source. A Backlight is the additional light source.
A Backlight can be a CCFL, (or more than one), or a series of LED's used as lights.
The Dell Vostro a860 Notebook PC uses one CCFL, for a Backlight, OR there are Vostro a860's that use LED lights.
(If you replace the LCD screen, make sure FIRST of what type of Backlighting it uses)
A CCFL is a Cold Cathode Fluorescent Lamp. Similar to Fluorescent lighting used in homes, and businesses, but on a MUCH smaller scale.
[Average thickness of a CCFL is 2mm. That is a little larger than 1/16th of an Inch.
Average length is almost as long, as the LCD screen is in height ]
A screen Inverter is used to convert the power from the laptop, for the Backlight, and LCD screen.
Most of the time the fault is the screen Inverter.
The Vostro a860 Notebook PC's, that uses LED's as a Backlight, MAY also use a screen Inverter.
For your problem it could be the screen Inverter, but I lean more towards the LCD screen itself, is the problem.
How to test a screen Inverter? Requires a very sensitive multimeter.
For a layman who does not have access to a sensitive multimeter, the method is to just replace the screen Inverter, and see if it is the problem.
'Parts changing', I know, but if you do not have the proper equipment to test with?
Screen Inverter replaced, and problem still persists, replace the LCD screen,http://www.laptopscreen.com/English/model/Dell/VOSTRO~A860/
For additional questions please post in a Comment.