Hello, I have an iMac that wont start up anymore. You can see it trying to load the OS, with the apple logo and loading bar. However it stops midway and powers off. What I did prior to the problem: I reinstalled Yosemite and transferred files from my TimeMachine backup into my user folders (Images, Downloads, Documents etc), as well as photos from an SD-card. When I restarted the machine the problem presented itself. Is it possible that copying corrupted files can cause this?