I decided to bite the bullet and replace my aged iMac with a new one, so I sprung for a refurb- 27-inch iMac 3.3GHz Quad-core Intel Core i5 with Retina 5K display (october 2015). Set the machine up and started a time machine restore, only to have the machine randomly re-boot after about 20 minutes. rebooted everything and re-started the time machine restore, only to have the machine again reset after about an hour in. I spoke with Apple and they just told me to take it in to the Apple store and have them look at it. No way I'm keeping a refurb that has issues right out of the box! If they didn't figure out the problems on this one before, I'm not going to bank on them figuring it out now. So refund it is. I had the machine shipped 1-day, so it cost me $40... they told me that I will not get my shipping costs back even though the machine they sent me is defective. After dealing with this for hours on end and accomplishing nothing, I'm completely frustrated. I've never been a person to go for a refurb, but everything I've read on here tells me they are reliable. I guess it's just my bad luck!! Now I have to drag this thing into the Apple store for a refund tomorrow. UGH. And the worst part? I'm eating the $40 and will have no computer. Thanks, Apple!