my MacBook is a bit too slow for me so I'm looking to sell it. I'm trying to wipe it so it's ready to set up for the new owner, but after erasing everything on the hard disk I'm now trying to reinstall El Capitan OS X but it takes hours and starts with 29 hours remaining, and then slowly increases up to 62 hours (sometimes more) and then it randomly stops and says it failed, so I should try again. And every time it does the same thing.
Any known reason why that's happening?
Edit: I have an old white MacBook that came out mid-2009 but it has recently been refurbished. 4 GB RAM. To get here I pressed Command+R during restart, clicked on Disk Utility and erased what was on the Macintosh HD disk, and then tried to reinstall OS X in the same menu.