Desktop

You should check the bios to see if it has been set to display an external monitor or in a power saving mode that blanks the screen. Then check to see if the external monitor will work on the laptop. If the external monitor does not work, then your video circuit on the motherboard has failed.

When I connect an external monitor to the laptop, it displays well.

You could also check the power settings for the display. Most laptops dim the screen when it is using battery power rather than an AC outlet. Failing that, the display may be on its last legs.

There should be a combination of keys that allow you to choose viseo output
internal - external - both
These keys are usualy [Fn] and [F7] or [Fn] and [F4]
try cycling round the options to see if it makes any difference - its a quick and easy before getting external monitors etc!

Sounds like your back light tube or the high voltage board is failing. Possible you have a wiring harness problem, but that would be an outside chance.

You need to have it repaired,

Vickie