Problem: When holding down alt on boot, I can only see my windows partition, and I can only boot to Windows 8.1. Process To Get To Problem: Brand new Samsung 840 Pro SSD installed, Made USB Installer for Mavericks, After installing, I immediately ran bootcamp at 50/50 partition, with win 8.1 installer on a USB flash drive ready. Once both were installed, I primarily used windows 8.1, and ran Samsung Magician with the aim to test and improve performance. I enabled Rapid mode, and over provisioning. And now I cannot boot to Mac OS X. I've tried: Disabling Rapid mode, and over provisioning. Running Disk Utility from USB Installer. Couldn't run 'Repair Disk', it gave some error message about backing up my data asap, and then formatting the drive. Reinstalling Mac OS X. But upon clicking install, just after verifying with Apple, it tells me to contact AppleCare. I'm currently typing this on a USB boot of the drive I removed from my iMac, and can see in Disk Utility that the drive is visible, and appears to have 3 partitions that are all dismounted, and read out as "disk0s2", "disk0s3" and "disk0s4"... these are greyed out texts under the hardware name of the drive: "512.11 GB Samsung SSD PRO Series Media" If I select the drive (not the partitions) and click "Repair Disk", the log box populates, and a pop up says, The log then reads as: If I select "disk0s2", and press 'Repair Disk', the log box populates, and a pop up says, The log then reads: The same happens for the other partitions, except "disk0s4"'s log appears as: The messages otherwise appear the same... I'm really stuck, and hoping for some expert advice. I'm familiar with terminal commands, and very confidant with making alterations. I'm sure theres some terminal command I could enter to fix all this, right?