Q: OS X Could Not Be Installed on Your Computer!

got to recovery but got "error occurred while preparing the installation" when I tried to reinstall Yosemite

Try running Apple hardware test

Using Apple Hardware Test

Try to force your Mac to boot into Internet Recovery by holding down Command+Option+R at startup.

I'm in the same boat but never used Time Machine

Obviously there should be an Exit Back to Yosemite button with El Capitan! 

OS X could not be installed on your computer

These problems could be a sign that disk drive is dying. I suggest you keep a close eye on it for any errors and also make sure you have plenty of current backups.

I'm getting this error too. So reformatting is the only solution to this problem?

Yes, I would try reformat and install EC.

i ended lip installing El Capitan on a 16GB SD card and then ran Disk Warrior to fix the HD.  I was then able to install El Capitan onto the main drive.  I don't know why Disk Utility didn't work and Disk Warrior did.  Cost me $130 but feel like it saved a ton of photos that I hadn't backed up for about two months.  I'm goingto start using Time Machine from now on. It's a life saver.

I ended up reformatting my Macbook Pro, more than 2 years of my personal files now gone,

You have never tried to use backup software to protect your data?

You are the only one that can be blamed for your lose of data since you did not implement a backup plan.