Some more details- My machine has gradually been getting slower over the past year. I'd been getting the spinning beach ball-o-death more frequently. Safari would often hang and then shut down unexpectedly; which is not too unusual, but it began to happen more and more frequently.
I usually leave my machine on all the time, and for the first year or so, I'd only need to reboot maybe once every few weeks; but increasingly, I'd have to reboot it more and more, to regaine performance, until it got to the point I was rebooting several times a day, depending on what I was doing. Usually it was Safari that cased most problems.
A couple days ago, it started as usual. I'd been running several apps; Photoshop, Dreamweaver, Fireworks, Safar- with about 6 tabs open, and Firefox with about one or two tabs. Things were running kind of slow, which wasn't too surprising, considering all I had open. But then in photoshop I got a strange reaction when the workspace window [not the whole screen] dimmed by about 90%. I could still barely see everything but for a few random bright red and green pixels outlining the image I was working on. Then it returned to normal after about 30 seconds and I saved my work. [Thank God]
Then I swiched to Safari and got the beach ball, so I switched back to the other open apps to wait for Safari to catch up. Then began a cascade effect as the other aps began to hang, until the entire system was hung up. The cursor still moved, but no repsonse to anything I clicked on. If I'd wait, about a minute later some things would repsond, but it just kept gettinng worse.
I was prepairing to shut everything down to reboot when unexpectedly, the screen went dark, like I'd accidentally moved the mouse to a screen sleep corner, and then turn back on. It did this several times, ...off, then on, ...off then on. Then the screen went completely dark, forcinng me to reboot with everything left open.
Upon restart, I got the chime and grey Apple screen with the spinning gear. The gear spun for about a min or so, I could hear the drive spinning away and the read head accessing, then I got a dark, "curtain" that slowly decended from the top of the screen, and a multi-lingual message popped up, telling me to restart my machine.
Every time I restarted, I'd get the same. Grey Apple screen, spnning gear, hard drive working away, then decending curtain and kernal panic
I tried safe boot; I tried holding the "c" key to boot from the install disk and got the same response every time. Grey apple screen with gear spinning for a couple mins then Kernel panic.
I even tried holding the option key which brought up the screen to choose which boot drive to start from. I'd choose the DVD and hear it doing it's thing, but after several mins, kenel panic, though it did take a little longer than when I tried booting from the internal harddisk.
I zapped the PRAM. I replaced the RAM. I replaced the battery on the mother board. I unplugged all periferals and turned off the local wifi... all with no results. Just the same startup with kernel panic before it ever reaches the log in screen.
One time at startup, all I got was a black screen with continuous chimes, over and over and over, so I had to turn it off. When I turned it back on, it did it's normal boot to spinning gear, then panic before the login screen ever shows.
After trying everything I mentioned above, I called Apple support and was told I'd already done everyting they would have suggested and that my next move was to take it in to the store.
When I got to the store, it started doing the constant chiming with a black screen again. No matter how many times I treid, nothing but repeated chimes. I couldn't even get the grey Apple screen to show. The guy there took it in back, emerged 5 mins later and said it had to be sent back, most likely needing a new logic board.
When I got it home, I was able to boot it again and do all I did before, but still gettinng the kernel panic before the login screen. I even tried booting from a copy of Disk Warrior someone gave me, but when I incerted it and held down the optioin key at start up to get the "choose a boot up drive" screen, only the hard drive would show up, not the Disk Warrior DVD. I put the Apple intall disk back in just to see if the DVD was still working, and it showed, just no Disk Warrior.
Not sure what more I can tell you. So what are my options? I *really* need to save my machine. I'm a student and do freelance projects and need my machine for school and work. I'm dead in the water here. HELP!
. Maybe it's that I've owned a lot of it, but I swear I've seen a lot more Apple stuff break than PC stuff in recent years. Airports, logic boards, fried gpus, displays, etc. The older cinema displays had parts fail that I've never seen fail in other displays. 
