iMac 24" alu shuts down for no reasons

[virusbeatbox]

Hi!

I'm having troubles with my 3-year old iMac 24 inch. Last evening, i was just surfing the internet like Facebook and MacRumors when suddenly the iMac turned itself off for no reasons. I didn't get any warning, it was like power got cut off.

All the other electronics like my desk lamp and charger of MBP was still working. So i rebooted the iMac and when I got on the desktop, it instantly turned itself off again! I thought it was the security when it's getting too hot, it shuts down by itself but, too hot of just surfing the web? My last try was a PRAM and SMC reset but nothing worked.

I left the iMac unplugged whole night and this morning still no progress. So, i performed a clean install but still, nothing really worked! After doing a Hardware Test twice, it stated there were no problems what so ever!
Booting into Safe Mode DID work but everything was really sloooow.

Then i realized I also had Windows 7 installed through bootcamp, booting into Windows 7 worked without problems. The iMac functioned as usual. Booting back into OS X the computer did not turn off this time, i left it like half hour, started iTunes, Terminal, Disk Utility, .. everything looked great until I started Safari. Without any good reasons the machine shut down again

Can please someone help me figuring out what this is?? I mean, everything works just fine when i boot into W7 but in Mac OSX, after starting Safari (same happens in Google Chrome), it shuts down again
I'm really confused what the problem can be.

I really hope someone can help me out!

PS: I was able to look into the console and saw this line of text just before it shut itself down. Maybe this helps fixing the problem?

Google Chrome[130] Unable to quarantine 'private/var/folder/fh/fhTr7y6PFMeidLMbQWcFRK+++TI/-Tmp-//com.apple.notify.130.1':1 (error suppressed)

 

[virusbeatbox]

Seriously, nobody has any idea what the problem can be? it's really important

 

[sukai]

I really have no idea what the problem could be, but if the browsers are causing this you should try uninstalling them both and reinstall them. Just something to try out.

 

[Roller]

Seriously, nobody has any idea what the problem can be? it's really important

Did a quick Google search ("imac shut down browser") and found some stuff about RAM and cache files causing iMac shutdowns. Do the same search and follow the most promising links. Good luck.

 

[virusbeatbox]

Thanks! I tried the cache removal and also the SMC/PRAM reset again but still no success :S

I just booted up the iMac and leaving it alone. It doesn't shut of if i leave it but when i start opening Safari or scrolling inside a web page, it turns itself off again... really frustrating

 

[Roller]

Have you tried another browser (Firefox)?

 

[virusbeatbox]

Have you tried another browser (Firefox)?

Jep, just tried it on Firefox but still the same issue. I also formatted my external HDD and installed OS X on it. After booting from that disk, going on Safari and opening a Youtube movie, the iMac shut itself down again. Now at least I know it has nothing to do with the internal HDD.

I'm starting to worry it will be the Graphics Card .. Has anyone an idea what the cost will be for a 3-year old 24inch iMac aluminum?

 

[peglegjack]

All I can say is that I have a 20 in. Mid 07 iMac that shuts down every few months or so when I'm just doing whatever on my computer, it can be anything. But I know for a fact that anytime it does that is because I've used the computer so much in a short period of time that it shuts down from the heat.

So maybe the computer is overheating. But yeah there's some thread out there that might say something about the logic board. I've never really bothered honestly, it's 5 years old at this point.