Fans won't stop running.

Run Apple Hardware Test in Extendedat least 2-3 times. The link to AHT is:

http://support.apple.com/kb/HT1509

Also there are numerous methods of resetting the SMC on Macs, the methods vary by what model you have. Because you didn't state the SMC reset process you used below is the correct method for an Intel based iMac.

SMC RESET

• Shut down the computer.
• Unplug the computer's power cord and all peripherals.
• Press and hold the power button for 5 seconds.
• Release the power button.
• Attach the computers power cable.
• Press the power button to turn on the computer.

PRAM RESET

• Shut down the computer.
• Locate the following keys on the keyboard: Command, Option, P, and R. You will need to hold these keys down simultaneously in step 4.
• Turn on the computer.
• Press and hold the Command-Option-P-R keys. You must press this key combination before the gray screen appears.
• Hold the keys down until the computer restarts and you hear the startup sound for the second time.
• Release the keys.

Sometimes it takes 2-3 attempts for the SMC to reset, that is what I would recommend doing first as it's the quickest thing to do. If still no joy then run AHT.

Based on your description I'm assuming you have a mid-2010 model iMac.

With the hard drive fan running at max RPM it indicates that the system is getting faulty or no hard drive sensor data, possible due to a disconnected or damaged sensor cable, or a hard drive where the internal temp sensor is not functioning properly. Has your system recently been opened for servicing or upgrades? If it has then you may want to take it back to have the hard drive temp sensor cable inspected. The sensor cable is a two pin cable that goes between the hard drive and the logic board.

Not quite the same issue but came home from work and heard a load noise in the office. It was the fans on my new iMac (2.7 GHz IC i5, 27 monitor) couldn't get it to power down. Pulled power coard for 20 seconds and plugged back in and fan started running hard again. Unplugged and let sit for 2 hours, during that time discovered there was a power outage earlier in the day here ay house. Plugged back in (surge protector) and is running normally.

Anything I should check out? Should I do the SMC Reset as listed above?

Thanks

dalkire wrote:

Not quite the same issue but came home from work and heard a load noise in the office. It was the fans on my new iMac (2.7 GHz IC i5, 27 monitor) couldn't get it to power down. Pulled power coard for 20 seconds and plugged back in and fan started running hard again. Unplugged and let sit for 2 hours, during that time discovered there was a power outage earlier in the day here ay house. Plugged back in (surge protector) and is running normally.

Anything I should check out? Should I do the SMC Reset as listed above?

Thanks

Yes it would be a good idea to rese the SMC however I would also begin looking into a UPS. Sudden power surges can damage electronics and a UPS will provide enough power to do an orderly shutdown in the event of another power outage, even if you're not there. To be honest you dodged a bullet, next time you may be as fortunate.

Thanks I Followed SMC reset and it worked, I have another problem My iphotos will not open any more, what I was doing was trying to copy my pics to a DVD so I could reset my computer beucse I could not open my time machine, but what i was really trying to do was to back date my computer as to reset, I reinstalled the original iMac application DVD andMac os X install DVD, then that when my computer fan would not want to shut off,

any help out there PS