Screen goes dim and bright

Go to settings, Power Saving Mode, If the brightness is checked uncheck.

Please connect it to external monitor. If it is not affected there. there, it could be an issue with backlight or inverter.- a hardware issue.

Sorry to hear that, Paul. As far as notebooks displays go, the light behind the screen is the part most likely to go out. It generally does just that: it just goes out, though the screen itself works (the LCD is still generating a picture, which you said you can still see). Whether you run it dim or bright doesn't play much of a role.
Another inverter replacement is probably needed here, with the light itself (what the inverter is powering) an somewhat less likely explanation. In any case, the notebook will have to be opened up to do the work, where is where a lot of the cost comes from (unless you or a friend is doing the work for you).

Good luck!

you have a drain on the battery. take the positive battery post off and connect a test light between the battery post and the cable. it should be very dim. if it is bright you have a short somewhere. make sure the doors are closed and take out the under hood bulb. if your test light is bright, start pulling fuses out untill light goes dim, then whatever fuse you removed to dim the light that will be the circut that is affected.

Your screen is faulty... possibly the backlight. You will need repair or replacement.

ok , you have checked the brightness settings, check battery power settings as well. you may have to do a hard reset so back up your info. If doing a hard reset, pull the battery and charge it on its own if you have a cradle. Hope this works for you

How long before it goes dim?

Does it start strong, then dims right away?

I figured it out myself. R243 was intermittently open. Replaced it, and now we can watch the Super Bowl.

Try Pressing the Option button and then P to bring up the Adjust Brightness control enabling you to dim or brighten the screen.