MacOS X el captain

How far does the install get and what error is given when it fails? If no error, then how does it fail?

If the install failed at Stage 2 which occurs after the initial copy stage and reboots for Stage 2. It sounds like you may have failed at Stage 2. You can try booting into Safe Mode in case you have some third party software installed if you were only reinstalling macOS over top of itself which will disable the third party software which may allow the install to finish.

Also, why were you reinstalling macOS? The same problem may be affecting the reinstall process.

Did you perform a clean install by first erasing the whole physical drive or did you just reinstall macOS over top of itself? If it was a clean install, then you likely have a hardware issue of some sort. A failing hard drive is the most likely possibility. You can try running the online Apple Diagnostics to see if any hardware issues are detected. Unfortunately the diagnostics don't detect most drive failures. There are other ways of checking the health of the hard drive if you are interested.

Also, disconnect all external devices in case one of them is causing a problem.

FYI, you should always mention the exact model of the Mac you are using as each model has their own unique issues many times. You can get the exact model by entering the system serial number here:

Check Your Service and Support Coverage - Apple Support

Shutdown the computer even if you must use the Power Botton.

Question ?

Reinstall implies your were in Recovery Mode and chose the option to Reinstall OS X. If that correct ?

below is not specific to El Capitan but the Reinstall aspect is important