My laptop screen goes black when plugged in

So when i plug my laptop the screen goes black. everything still works, but the screen blacks out. when not plugged int he screen is very dim, but i can still see it. Any ideas? Its a Dell latitude 3440 running win 7.

check your power manager settings, it might be set to dim the screen plugged in to the wall

So I fiddled with the settings, even though i set the brightness to max it still is freaking dim. and it still goes black when i plug it in.

Chances are your inverter board or backlight has gone on your laptop (inverter is more common).

Is it expensive?

Nah, parts are pretty cheap, it's more a case of whether you can still get them. It's a fairly easy repair on most laptops,definitely worth seeing if you can get the parts rather than replacing it first.

Ok, Ill have to give my computer guy a call tomorrow.