My Mac Book Pro does not even start after latest Mountain Lion update, any ideas?

Thank you very much for your help. What is happening to my MBP is that it actually turns on But remains in the white page of the startup And nothing else happens for the next 30 min (the largest amount of time I have waited). Something similar happened with the mountain lion update inmediately before the last one, But the delay between turning on And getting the system completely function was around 10 min. What I did that time was to redownload mountain lion And Problem solved. But this time I never got the system functioning. What i have done is restarting from internet with holding opt-cmd-r while turning on the computer And when prompted recovering with my lastest copy on time machine. I will be updating to tell you what results I get.