Lenovo Thinkpad T400 can’t adjust screen brightness after stand-by is another problem many people complained. Someone who hasT400 LED with Windows Vista Business SP1 installed said that sometimes his laptop can’t adjust screen brightness, neither through the Fn-Keys nor via the power manager.
The problem of can’t adjust screen brightness on T400 after using stand-by mode, might occurs caused of the Windows related software as many T400 users can fix it only by reboot the machine. But before reinstall or upgrade the system, better check the computer’s power, does this problem occur when on both battery and when plugged in?
Just for notice, you can set the T400 screen brightness through the Power Source Optimized battery plan preference. And then try setting all dynamic brightness controls to disabled. And then after rebooting your T400 machine see at the laptop screen, are you still can’t adjust screen brightness? If it so, updates Windows Vista Business SP1 to SP2 should be resolve the problem.
