I have a Dell Inspiron 8600, it's 3 going on 4 years old. I believe the screen is an SVGA+. Lately the screen, when on max brightness, whether or not it is plugged in, will occassionally dim to a lower level of brightness randomly, lasting for various periods of time between a few seconds to 15 minutes. Is this likely a hardware issue, to be expected with an older machine, or does it portend more problems to come? Should I be looking into my warranty and is there anything I might be doing wrong that's causing the problem? I'm worried about the warranty tack, i've heard that Dell will occasionally replace screens of the wrong type (i.e. an SVGA instead of an SVGA+).

I am afraid that there were issues with those-- video-card overheating issues-- probably not worth the cost to fix.

Dell Inspiron 8600 Issues

Inspiron 8500/8600 Video Upgrade

Do I need to be worried about it going out completely on me all of the sudden any time soon?

I am afraid that that would be impossible to predict-- it might die today,next week, or next year... I'd treat it as a signal to put aside cash for replacement,
If it starts happening more frequently-- you know it's about time.
Keep your backups up-to-date.
Why I don't do laptops
1) I have no need for portabilty-- and ventilation / heat control are often issues
2) They lose value overnight
3) they are not usually worth repairing-- I looked at repairing yours--you have to take the keyboard out just to acceess the video card--