My girlfriends iMac has been just shutting down periodically. There seems to be no rhyme or reason as to when it does it but it seems to go in spurts. It will keep shutting down in a period of like 2 or 3 days and then be fine for a couple of weeks. Then start acting up again. Just recently its had a couple of times where it won't even start back up, we've had to pull the power cord for a little while and plug it back in and then it starts back up. The serial number doesn't fall within the range shown for the ones with the power supply problem. So my concern is when we call for support how do we guarantee they won't charge us for the call?