My HP lap top screen is very dimm when it is connected to the AC transformer and it is bright if it is not , so what is the problem.? When it 's not AC connected , the battery power will be drained within 30 min eventhough it's fully charged.

try this

press f3 to increase the brightness, f2 to decrease

or,

hold fn key and press f3 to increase the brightness
fn+f2 to decrease

let me know if it works

Just go to power options in control panel and click change plan settings of you current plan and move the slider right to increase brightness.Please note the left slider is for when on battery while the right slider is for when connected to AC power. Finished.I hope it helps

my lap hp pavalion dv4 2126tx........
i am working in win 7 os .when the lap is connected with ac charge plugin its working normally....if the ac plug in disconnected lap becoming death slow

Go into display settings and click on advanced settings, then click on the color tab. There is a slider in there that controls the screen brightness. This is for windows xp but vista should be similar.

are you using xp vista or windows 7

xp might be the screen saver settings. vista or windows 7 check power options in search

try contrl alt del at same time hold for 5 sec if that does not work take batt out hope this helps

You cannot adjust the brightness with the key board. If the brightness control on the monitor is not working. It may due the defect of screen control on the flyback transformer. You have to replace the flyback transformer (FBT)

there should be brightness adjustments if you hold down the Fn button and look at your function keys F1,F2,F3,etc. There should be "cones" with plus and minus signs to adjust brightness

make sure the other side of the adaptor is also pushed in fully...i hope this can help

can you boot with the AC adapter? maybe the battery is completely dead.