Hey guys, I need some help. I'm a PC tech, not a Macintosh tech, but I can figure things out. My friend has a 27" iMac and we're trying to fix it. He updated it to Yosemite but realized he wanted to go back to Mavericks. Now, I'm a little vague on what he did, since I only came into the picture once he was having issues. I think what he did is he had a time machine backup, and he restored it. I think that gave him issues, and somewhere along the way he partitioned the drive or deleted some partitions (he was also running bootcamp with a Win7 installation) Now, when you turn on the iMac, the screen turns on and is grey, there's no chime sound, and the screen goes black. I've tried to boot from a burnt OS dvd by holding the C key down, but it won't boot... not sure if the dvd is badly burnt, don't have an original. When you hold down the options key upon boot up, a lock shows up. He doesn't remember the password! Form what I've read, that's a firmware password? Now, I've read that you can clear that password by booting into your recovery partition, but I think he deleted his recovery partition when he was playing with the time machine / bootcamp Windows 7. I've pulled out the hdd, and the iMac turns on, but I get a folder with a question mark flashing - probably because it can't find anything to boot from. I'm pretty sure it's not a hardware issue, but an OS issue. I'm running out of ideas. I don't have another Mac and I don't have original media to install from.