Hello. I have a problem concerning my Macbook Pro 17" (early 2009) running Yosemite. The story: It was running well until yesterday. I wanted to reboot my system, however, during start-up, the progress bar under the Apple logo goes half-way (very slowly), after it turns into the Prohibitory Sign. I have a Windows 7 bootcamp partition as well, which starts up just fine. Within Bootcamp, i can acces the OSX partition as well, so i don't think there is a HDD problem really (however, correct me if i'm wrong) I have researched the internet for hours and hours but couldn't find a working solution as of yet. What i have tried so far at startup: - PRAM reset (multiple times) > Does not make a difference. - Command + R (Recovery Mode) > Does not start. Just Apple logo > Prohibitory Sign again. - Option (Startup manager) > Only my OSX(obviously not working) and my Bootcamp(Working) partition is showing - N (Netboot) > Shows a picture of a Globe blinking for a few times and disappears. After, same as before (Apple logo > Prohibitory sign) - Shift (Safeboot) > Doesn't work, Safeboot does not start - Command + V (Verbose mode) > Shows the usual white text, but gets stuck on "Still waiting for Root Device" - Command + S (Single User Mode) > Same as Verbose Mode It is worthy to note that i do not have access to an Installation DVD as i have purchased this MBP second-hand and a disc was not provided. Also, i did not install anything while using OSX yesterday (when it was still running). Any ideas? Thanks.