Yesterday I installed Windows 7 using the Boot Camp Assistant. I switched back to OSX by holding down option while booting, and a few hours later put the computer to sleep from OSX before going to bed. This morning when I went into my office, the iMac was on and had a black screen with the text, "No bootable device found." I pushed the power to turn it off and back on, and it successfully booted into Windows. I thought that was weird since the last OS I used was OSX. So, I restarted again and booted into OSX with the option key. Chrome loaded and had an error that it hadn't been closed properly. Everything is working fine, but it makes me wonder what happened while I was sleeping. My iMac must have turned off and rebooted into Windows, but it didn't see the Windows partition and gave the error. I just went into Startup Disk to make sure that OSX was selected, and I noticed that both OSX and Windows highlighted. I selected OSX, so I'll see after switching to and from Windows again how it affects the startup disk selection. With this being a new computer, it just makes me paranoid since I have the Fusion drive. My iMac is hooked up to a UPS and I didn't have a power outage for it to turn off.