What to do if your Mac won't turn on.
Different ways to gain access to your mac
1.Pressing key " D " runs hardware test for mac
2.Pressing key "C" to do OSX test
3.To format the Macintosh HD( to erase and do a clean up need to go inside OSX recovery), --> in order to do a OSX recovery pressing
COMMAND and key "R"
4.Press SHIFT in the keyboard to enter in to safe mode
5.Press OPTION in the keyboard it prompted for 3 options Macintosh HD,recovery 10.10.1, OSX installation DVD
Please refer to the link http://www.dummies.com/how-to/content/how-to-use-startup-keys-to-resolve-mac-os-x-boot-p.html