Try running it with only one stick of ram at a time.
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Problem might be your UPS
My new Intel iMac worked for 3-4 months just fine and then started exhibiting symptoms just as you describe. I finally traced the problem to the (new) UPS I purchased along with the iMac. I have an APC Back-UPS BE550R. I discussed the problem with APC tech support and they researched the issue and determined that the new Intel iMacs probably need the Smart UPS series because Intel Macs require a transfer time of 4-5 milliseconds but the Back-UPS series has transfer rates of 8-10 milliseconds. Be advised that the Smart UPS series is quite a lot more expensive than the Back-UPS series.
For the record, he said that my 2.8 GHz 24" Intel iMac has a maximum wattage rating of 280W and he concludes that I need a UPS having at least 350W capacity due to start-up surges. I calculated that my iMac would run for 9.5 minutes on the recommended smart UPS SUA750 ($320) in the event of a power outage. I haven't purchased a new UPS yet as I'm hoping to get feedback from others whether or not this makes sense.
Meanwhile, my Intel iMac has been plugged into the wall socket for a month now and I haven't experienced any further problems.
My new Intel iMac worked for 3-4 months just fine and then started exhibiting symptoms just as you describe. I finally traced the problem to the (new) UPS I purchased along with the iMac. I have an APC Back-UPS BE550R. I discussed the problem with APC tech support and they researched the issue and determined that the new Intel iMacs probably need the Smart UPS series because Intel Macs require a transfer time of 4-5 milliseconds but the Back-UPS series has transfer rates of 8-10 milliseconds. Be advised that the Smart UPS series is quite a lot more expensive than the Back-UPS series.
For the record, he said that my 2.8 GHz 24" Intel iMac has a maximum wattage rating of 280W and he concludes that I need a UPS having at least 350W capacity due to start-up surges. I calculated that my iMac would run for 9.5 minutes on the recommended smart UPS SUA750 ($320) in the event of a power outage. I haven't purchased a new UPS yet as I'm hoping to get feedback from others whether or not this makes sense.
Meanwhile, my Intel iMac has been plugged into the wall socket for a month now and I haven't experienced any further problems.
I stumbled upon your original thread at <http://forums.macworld.com/message/643752> while researching UPS requirements for my new 24" iMac. I had just purchased the APC BE550G, and was rather upset to read what the APC tech had told you. Based on that "advice," I "upgraded" the BE550G to the BE750G, hoping that the tech's assessment may have been correct regarding the power requirements, but incorrect regarding the transfer-time requirements.My new Intel iMac worked for 3-4 months just fine and then started exhibiting symptoms just as you describe. I finally traced the problem to the (new) UPS I purchased along with the iMac. I have an APC Back-UPS BE550R. I discussed the problem with APC tech support and they researched the issue and determined that the new Intel iMacs probably need the Smart UPS series because Intel Macs require a transfer time of 4-5 milliseconds but the Back-UPS series has transfer rates of 8-10 milliseconds. Be advised that the Smart UPS series is quite a lot more expensive than the Back-UPS series.
For the record, he said that my 2.8 GHz 24" Intel iMac has a maximum wattage rating of 280W and he concludes that I need a UPS having at least 350W capacity due to start-up surges. I calculated that my iMac would run for 9.5 minutes on the recommended smart UPS SUA750 ($320) in the event of a power outage. I haven't purchased a new UPS yet as I'm hoping to get feedback from others whether or not this makes sense.
Meanwhile, my Intel iMac has been plugged into the wall socket for a month now and I haven't experienced any further problems.
My experience so far with the 750 has not been entirely satisfactory: When the iMac is shut down for the night, the UPS begins to make a “clicking” sound every 10-15 seconds (as if it were switching on and off). The sound continues to repeat itself until I turn on the iMac.
I’m a bit concerned that this may be part of the transfer-time issue that the APC tech had mentioned. However, it happens only when the iMac is turned off (but the UPS still is plugged in and receiving utility power), which seems contrary to the condition described by the APC tech. (In other words, the UPS is not being told “Hey, we’ve lost utility voltage, and the iMac is ‘on’ and needs power.”) Moreover, the previous unit (BE550G) didn’t exhibit this behavior (it was always quiet). So it may instead be a defective unit.
FWIW, I initiated a thread about this in the Apple Discussions Forum (see<http://discussions.apple.com/thread.jspa?threadID=1577204>). So far, the responses I've received seem to reflect the belief that the APC tech is "full of crap." However, these responses seem based less on specific knowledge and more on anecdotal experience that may or may not be applicable.
Although the APC tech indicated to you that "...we now recommend a Smart-UPS for all Macs. Our UPS configurator is being updated to reflect this recommendation," the APC website has still not been changed.
Have you any further information?
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