Powering off for no reason...

Last night, my iMac started giving me some problems... It boots up fine, but after about 5 minutes it switches itself off! I then have to leave it for quite some time before I can power it back on - I'd guess at more than an hour. If I try to power it on before this point I get no response. It's an Intel iMac, 24" 2.8GHz and, unfortunately, it was bought September 2007 - so it's just out of warranty. Doh!

I'm going to try resetting the SMC tonight, and also try the Apple Hardware Test.

Just to clarify, this isn't a software crash that causes it to stop working, it actually powers itself off. It also doesn't seem to be triggered by any particular activity - I can leave it with nothing running and it will do the same thing.

Any ideas?

Power supply? Maybe a temperature issue? I have iStat Pro running on the dashboard and it doesn't show anything excesive.

Anything I can try before giving up and taking it to Apple

My first guess would be a possible temperature issue. You can try downloading and installing SMCfancontrol (I think it will work with iMacs) and setting the fans higher to see if that resolves the issue.

Thanks for the quick reply... Something else for me to try tonight. Just have to keep my fingers crossed that I can download it before it powers off again!!

If it is powering off that quickly more likely a hardware issue.

Installed anything new on it lately, such as drives and/or memory modules?

No, nothing new installed.

I tried resetting the SMC last night, so the fans would stay on constantly. I figured this would eliminate a temperature issue. However, with the fans running full speed from power on, it cut out after only a few seconds.

I may be wrong, but it seems like some kind of power problem to me. Either the power supply, or maybe something showing some kind of power fluctuation that's causing it to cut out to prevent any damage...

Anyway, with an iMac that will no longer boot, I guess I have no choice but to take it to a service center.

I guess that Apple Care extended warranty looks more appealing now. Shame I didn't take it out!!