How long does an ibook last?

I've had my ibook g4 since September 2005. It's been used for at least 4 hours/day since then, has been carried back and forth to school/work daily, and has been on various international journeys. I think I've taken pretty good care of it - it's always in a case when on the move, don't slam it down or put things on top of it, etc. I do tend to leave it sleeping instead of turning it off for days/weeks at a time though, maybe this caused some problems.

For the past month or so I've been noticing some problems - trouble with the power source (not a consistent stream of power, flashes back and forth from "plugged in" to "battery" when connected to the wall. Screen goes black with lines going down it, so I hold down on/off button until it restarts (and is normal again, this would happen every few days or so).

Last Friday, I was using the computer and it completely turned off. Not just the screen, the entire machine. It wouldn't turn on again all night. I took it in to an Apple repair place the next morning and left it. On Tuesday they called to say it was ready - they had to re-solder part of the DC jack. They recommended I purchase a new power cord, which I did. Nor problems yesterday. Today all the same old problems were happening, to the extreme! Flashing from dc power to battery continuously, screen went to black/lines (but machine still was running) 3 times within an hour. Power finally went, and now it's not getting any power - battery won't charge.

Is my ibook at the end of its life? Or is it worth paying for parts and labor to fix both the screen problem and the power problem? I'll do it if I'll be able to rely on the machine after that. But I don't want to pay $400 to then have to buy a new laptop in 2 months! It's $100/hour + parts to get it fixed again.

Thanks for any advice! I need a computer I can rely on apple: all the way of course, but the question is this one or a new one??!)

Thanks for your reply. No, no applecare.. I had 2 year, of course...

I did stop in at the store today and ask what they thought. They said I'd get a labor discount since they'll be redoing some of the work, but the screen issue is different than what they were addressing before so I'll have to completely pay for that. Plus parts for both issues and labor that goes above whatever discount I get. But they wouldn't get more specific until they open it up again, which I didnt want them doing until I think it over! And I was hoping to get some data out of it tonight, but it's completely dead so that's not happening

Thanks for the responses! I like the idea of a new computer, that'll be nice, and hadn't thought of selling for parts, that's a good plan.

It's frustrating though, shouldn't I be able to get more than 2 years out of a computer? Especially a mac, I thought they were built to last for longer than that...