If there are any keys with a blue sun symbol on them, try using them them with the Fn key. Otherwise, there should be a setting in the BIOS, but don't change any BIOS settings unless you are sure what they do.
Assuming the 2650 BIOS is the same one as the 9400, do the following:
Start the machine, and press F2 as soon as the Dell name appears. If you miss, shut down the machine and try to be quicker pressing F2
Use the down arrow to highlight Video.
Use the right arrow to expand it.
There should be two Brightness options - one for battery and one for AC power.
Highlight the one you want (use up/down arrows) and press Enter.
Use the left/right arrows to change the brightness setting.
Press Enter when finished.
Change the other Brightness setting if you want.
Press Esc, choose the option you want and press Enter (you can cancel your changes at this stage).
If you select Exit and press Enter, the machine should now boot with your new settings.
If the BIOS is different can anyone help who has a 2650???