iMac randomly restarts

i have an iMac 2.4gHz (20-inch mid 2007) which is currently with the apple geniuses. i've experienced the same problems as most have posted in this thread with random restarts at first, then the imac shutting down (no restart), and then not wanting to start up at all.

took it in once for the random restarts and not wanting to start up with apple not able to find anything wrong with the unit, but a little over a week later, not wanting to start up at all, and a quick shut down

i went threw all the steps from removing the third-party ram i purchased and putting in the standard apple ram to removing all plugged in usb devices (external HDD and printer).

was really frustrated when all this started and especially when they couldn't find anything wrong with it, hopefully they can find the issue and get it fixed as it is still within the first year warranty.

we'll see what happens!

so, i spoke with the apple geniuses and apparently it was the logic board (which is what they told me could be the problem when i first brought it in) and they've replaced it and are running tests on it. we'll see what happens when i get it this evening. hope that really fixes things.

anyone else have the logic board replaced and had the problem of restarts fixed?

so i got it back on friday (6/20/08) night, and have experienced a couple of restarts, at least three or four today (6/23/08). i have no idea what to do now. they even changed the dvd-drive as apparently test they ran after changing the logic board showed that was faulty as well. at least i am now able to start up the imac.

iMac is going back to the geniuses tonight! sigh, restarts started almost the day i got it back, and it would not turn on last night

got the imac back on friday (6/27) night and worked with it all weekend without any issues! they replaced the power supply and apparently the logic board again, but i think the person checking me out got confused.

i could really see a difference right away and it felt like when i first got it out of the box and started it up. hopefully this resolves things, but i am very happy for now as i can just tell there is a difference.

I just bought a imac 20" and it start restarding randomly and I took to the apple service support and they run the test and had in store for 24 hours and told me it was Logic card... and they will replace it...
Hope you could solve your problem with it

please please please!!!!!!!HELP!!!!
i have the same problem iMac randomly restarts.
hardware tests appears to be ok
when i verify permissions (private/etc/cups should be 0 and it is 26) i dont know if it has any reason??
my reseller 4 times gave me different reasons
1.power supply 2.hard disk problem 3.problem with safari 4.problem with 10.5.4 update
but i still have my imac restarting its self.
PLEASE HELP!!!!!!!!!!!!!OR GIVE ME POSSIBLE REASONS FOR THIS.
THNKS
(sorry for my English)