I am working on a Dell XPS M1210 laptop with a unique problem. The battery charges fine. The laptop works fine on AC power. When the AC adaptor is unplugged, the screen immediately goes almost dim. If you look at the screen, you can still see that Windows XP is working normally but it is like the screen has gone to its lowest setting possible. I have lurked the forums for the past two hours reviewing a large number of threads that were similar to my problem. I have already done the following:
1) Checked Windows power and display / video driver settings. These are normal and changing them has had no effect on the problem.
2) Upgraded to the latest video driver. No effect.
3) Tried Speed-Step on / off. No effect.
4) Checked BIOS settings for Power. On battery power, the screen brightness under bios is set to maximum. Normally it should be 3 but in Bios it is set to the max which is either 9 or 10 (the entire bar is full). Lowered screen brightness manually, then took it all the way back to 100%. Saved bios settings and rebooted. No effect.
5) All MS updates have been done.
6) Checks for virus / malware / spyware are all negative.
After lurking the forums and trying everything that I could find mentioned here, I decided to post this question because the original problem is apparently not responding to any of the suggestions / solutions that I've been able to read about and throw at it. When you remove the AC plug, the screen will go to almost dim. No amount of FUNCTION and Increase Brightness ("sun button") has any effect on the brightness at this point. The only way to get the bright screen back is to plug in the AC adaptor and then switch to external CRT and back again to the video display. The screen cycles and flashes and the bright normal Windows screen appears again.
Any ideas?