MacBook Pro 2009 problem

So I bought this MacBook Pro that worked and I tried to install OS X El Capitan but it just keep on saying there is no package eligible to install I contacted Apple and they told me to do this and do that, and then my system failed and it keeps on saying there was problem with restarting you computer please click a key to continue. I did and it gave me an error code once it has restarted and it went back to press a key to restart you computer and it will go back to the error code and it keeps on going in a loop never ending is there a way I can do to stop the loop and go back to my original computer screen?