headphones work for only a few seconds after plugging in

Double check things by using different headphones and/or cables to different sources ...a stereo for example. You may also try blowing into the jack (or using Compressed Air) as it may have become dusty somehow. If you're 100% certain it's not a problem with your equipment then def. bring it in to an Apple store to have them test it out. If it is a hardware issue then it'll be fixed.

Macbook 1.8-) Mac OS X (10.4.8) Week 38 base model w/1G Ram

Open System Prefs/Sound/Output and check that the headphones replace "Internal Speakers" when plugged in. The switching for headphones is under software control and not a simple break jack on the socket.

It's worth wiping the 3.5mm jack with switch cleaner/lubricant like WD40 to help the contacts stay clean.

Hope this might help,

John.

I did have a problem with missing sound which was cured by checking the HD/Applications/Utilities/Audio Midi Setup/Audio Devices and ensuring that the sample rate format was set to 44.100.0hz. This was a "No Audio on YouTube" problem but fixed when I found the Midi setting to be 96khz or similar.

My only further thought before dragging the machine back to the store is an OS reload.

My core duo was not behaving correctly out of the box and had several problems among which iSight camera on and not responding, so I did a clean install from disc of the operating system.

Tiresome I know but in my case it cleared everything and the Mac's been fine since.

Best of luck.

Brian, I forgot to ask, do the headphones always cut out after the same period of time from plugging in, or is that random?

Do the speakers cut in, or in a muted condition does the Sound panel still show headphones conected?

My point about switch cleaner on the headphone jack was as much a technique to get some lubricant/cleaner into the socket itself without spraying liquid into the hole. I mention this as tarnish on the socket from manufacture can play havoc with connections, and these little 3.5mm sockets are not usually of the highest quality.

Rather fear you have a more serious problem, and a return to Apple should be the next step after an OS reload.