Running a Imac Mavericks. I have attached a Mediasonic Probox 4 bay Hd enclosure with four Sata Hd inserted. Everything has been working just fine for the past 18 months when I set this up. About a month ago; one of the Hds quit showing up on my desktop and in Finder. However; if I should fail to eject that Hd properly; an error message will pop up stating that I failed to eject that Hd properly. Pretty hard to eject it when it doesnt show any where! I did some experimenting. I turned of the enclosure for a few hours and than turned it back on; and the said Hd showed up. However; I had the same problem later. I also removed the other three Hds and just ran the one in question. It showed. However; when I inserted the other three; I had the same problem. I tried connecting the enclosure to my MacBook Pro and nothing showed at all. However; that is a different problem for a different post. Any ideas? I suspect maybe a heat problem; and I will experiment with that. The Hd in question is the smaller of the four at 320 gig. I have already backed it up.