Q: El Capitan won't load

Hi,

Make sure your Mac meets El Capitan requirements >  Upgrade to OS X El Capitan - Apple Support

The installer should be in your Applications folder if it downloaded. Try signing out of the App Store, restart the computer, sign back in, and go to your Purchases tab to try the download again.

If that doesn't work, try downloading in the Safe Mode or another admin account.

Safe Mode

Safe Mode - Mavericks

Safe Mode - About

Safe Mode - Yosemite

Open the App Store then select Purchases then see if you can click Resume.

Or open Launch Pad from your Dock and try resuming the download from there.

Aside form that, if installed, disable anti virus software then try resuming again.

And, El Capitan requires about 9GB's of storage space. You can check available storage space in your Apple menu  > About This Mac > Storage.

Did you try the Safe Mode and another admin account?