Mac OS X Yosemite broke my iMac I recently tried to update my iMac OS to Yosemite as most people had already done it a while ago. 
it downloaded the package when rebooted to install it. It was stuck with error message. 

It looks as if there was an issue with hard drive preventing installation.
I was also unfortunate to revert the installation, hence end up loosing all my files as I decided to erase the disk and create new partition. 
Even after formatting the disk and using 'Reinstall OS X' from recovery mode; I am unable to complete. 

The screen doesn't seem to do anything stuck at 'Downloading additional components, it will automatically restart' I tried leaving it for few hours but no result.

Would someone please share your experience?
Try using Internet Recovery Mode instead of the regular Recovery Mode, and make sure that you formatted the right hard drive (in other words if you have an external hard drive plugged in, make sure that you formatted your actual hard drive, not your external one).

Here is some more info about different recovery modes from Apple's support site.