Okay so I have a 2009 iMac that I recently updated to Yosemite. It was working fine this morning albeit a little sluggish, then late this evening I wanted to get some work done but it was so slow I couldn't get anything to load. I decided restarting it would be a good first move being as it had cleared up slowness in the past but when I went to reboot I was greeted with a grey, flashing folder with a question mark in the centre. I have been trying everything I could think of all night to figure out what the problem is and have gotten no where. I threw my snow leopard disk in and went to disk utilities, it shows my DVD drive and another device called Media. I clicked get info and it came up with Partition map scheme: unformatted Disk identifier: Disk7 Media Name: Media Media type: generic Connection bus: SATA Device tree: IODeviceTree:/PCI0/SATA@1F,2/PRT0@0/PMP@0 Writeable: Yes Ejectable: No Location: Internal Total capacity: 0 bytes S.M.A.R.T. Status: not supported Disk number: 7 Partition number: 0 All the first aid options on disk utility are greyed out and unclickable and I'm officially at a loss for what to do. Any suggestions would be great, I'm hoping it's still fixable seeing as it was fine earlier today. I've tried all the basic stuff, holding option while booting, doing the command+option+P+R thing and so far no luck. It makes the chime when I turn it on and then it sits on a grey screen for a few moments before the flashing question folder pops up.