pressing "c" before you hit the power button?
The C key will do nothing unless you have bootable media inserted:
For the best experience with startup keys, press the keys immediately after the startup tone plays.
If not using bootable media, for Lion or ML, boot holding Command + R or Command+Option+R.
For the OP:
I agree with RRFS - give Disk Warrior a try.
When i switched on, the progress bar takes an age to get to 99% then the machine powers off.
By using cmd-r I was able to get to "osx utilities" which gave me 4 choices
1. reinstall from time machine - didn't set it up
2. Reinstall OSX - don't want to wipe the machine so haven't done this yet
3. Get help online - using macbook so don't need to
4. Disk Utility - that gave the above jpg
Burning a 'New Image' DMG of the disk onto an external drive and will see if that helps.
(tried making an uncompressed one, but it failed overnight, so going for the DMG)