Can't boot to Mountain Lion

Hi
I have a Mac Book Pro Retina with Mountain Lion installed. Yesterday I turned it off and when I have come to turn it on today it can't find Mountain Lion to boot from. When the white screen appears where there should be a Apple symbol there is a warning symbol instead. After this it goes straight to OS X Utilities and when I go into Disk Utility to verify/repair the disk it says that this is done successfully and yet it still won't boot. Holding option on start up means I can see the hard drive to boot from and when I select it, it just goes straight to the OS X Utilities again
I don't want to re-install OS X because there is some data on the hard drive which I need. Also I do have a time machine backup but again, I made it so some of the folders don't sync, some of which I need.
Before I turned it off I can't think of anything which I was doing to cause any problems. I was only surfing the internet and doing a bit of programming.
Is there anything which I can do to get access to the files I need? Also what has actually caused this?
Thanks

I was only surfing the internet and doing a bit of programming.

Click to expand...

Programming what? Sounds like you may have shut yourself out of Mountain Lion? Anyway, you shouldn't be afraid to reinstall Mountain Lion since it does an an automatic archive and install. In other words, it does not destroy your data or apps but should reinstall whatever went wrong with the system.

I was doing some stuff in C but I was only compiling the code, not actually executing it. I didn't realise that reinstalling mountain lion would keep my documents. I will give that a go.
Cheers