Hi, I also have a similar problem. I recently downloaded Parallels 10 for the first time in my mac working with Yosemite 10.10.3 and was unable to install windows. Despite "reading" the Win7 installation cd form the optical drive, and after introducing the activation key, no installation begins but an MS-DOS window is displayed triying to boot from any drive and and it says "unable to read an OS". Colud it be possible Parallels 10 isn't working with Yosemite 10.10.3? Any solutions?