I have an Inspiron 6000 with the ATI Mobility Radeon X300 display adapter.  After changing the battery, I have been experiencing problems with the backlight.  Periodically, the backlight will turn itself off.  The items are still displayed on the screen and visible if you shine a light on the screen.  The screen is just not lit up.  I have read numerous forum posts about replacing the inverter, LCD screen, etc and I just want to make sure I find the definitive problem before I waste any money. 

When it is hooked up to an external monitor, the computer works fine.  Also, when toggling the FN + F8 key, the laptops LCD display will sometimes turn back on.  My son played around with the ATI software and set it up for single monitor operations and it seemed to work normally for a full day or so.  I have set all of the options in Power Options to “Always On” so the screen should stay on.  The screen saver is not an issue.  During this time, I ran the Dell Diagnostics and all of the Video Tests worked just fine. 

This computer also has a faulty headphone jack (no sound via laptop speakers unless jack is pushed upward).  I took the computer apart to try to repair the faulty connection with no luck.  When I reassembled it, the intermittent backlight problem returned.  When it works, it looks good (normal).  There is no reddish tint or anything else indicated. 

I found another post about the magnetic reed switch in the palm rest possibly causing this problem.  I was able to duplicate this by swiping a small magnet over the palm rest just below the mouse buttons.  Swipe it once to make the computer go into standby mode, and swipe it again to make it wake up.  Sometimes this will make the video reappear upon reawakening.  It goes out again shortly thereafter though.  It seems as if something is telling the backlight to turn itself off.  As I said, when it works, it works just fine. 

Is the problem with the backlight, inverter, magnetic reed switch in the palm rest, some kind of software setting in the ATI or Windows XP software, or something totally different altogether?  There seem to be a number of possible problems, and I am trying to eliminate them before I spend any money on this old machine.  Thank you for any help provided.