OS X El Capitan has made my Mac Book Pro to Hang

I updated my Mac Book Pro 13" recently and was happy with the all new OS X El Capitan. For real this update has the best User interface so far and I was happy to use it. But after three days, when I powered on my computer, it just picked my log in details and hang for the whole day without booting up. I was forced to call in a Mac technician to format my Mac Book Pro and return me back to OS X Yosemite. Please what could be the issue and if any would you kindly update it so that we may not be locked out of the enjoyment people are having with OS X El Capitan.