From macos yosemite can't install my mac os x el capitan keeps crushing. What shall i do?

OS X El Capitan - Technical Specifications

General Requirements

• OS X v10.6.8 or later
• 2GB of memory
• 8.8GB of available storage
• Some features require an Apple ID; terms apply.
• Some features require a compatible Internet service provider; fees may apply.

Mac Hardware Requirements

For details about your Mac model, click the Apple icon at the top left of your screen, choose About This Mac, then choose More Info. These Mac models are compatible with OS X El Capitan:

• MacBook (Early 2015)
• MacBook (Late 2008 Aluminum, or Early 2009 or newer)
• MacBook Pro (Mid/Late 2007 or newer)
• MacBook Air (Late 2008 or newer)
• Mac mini (Early 2009 or newer)
• iMac (Mid 2007 or newer)
• Mac Pro (Early 2008 or newer)
• Xserve (Early 2009)

What exactly are you trying to do? Go back to El Capitan? Do you have a backup of your files? Like Time Machine. Because if you are trying to backup to El Capitan, you will have to erase your drive and install off a El Capitan bootable installer.