Dell Inspiron 640m - LCD Display - Dimming

My Inspiron 640m is 5 years old. Out of warranty.

When I bootup the laptop, the boot screen appears and then it goes completely black/dim.

Connected an external monitor and found that everything was working properly on external monitor.

Searching forums, found that I need to replace LCD Backlight and/or Inverter.

My LCD is: 14.1 INCH TRUELIFE,WXGA+,I640M/E1405

Part# given on the invoice was 465-4186 but could not find it.

Can anyone help me in order these parts or solving the problem.

Many thanks in advance.