Try booting into single user mode instead. You don't need the install disk.
Turn off your comptuer. Restart it holding down the "command" and the "S" key on the keyboard. Keep them held down, until you see a black screen with white writing.
As soon as you see the black screen, release the keys.
You now need to type the following:
/sbin/fsck -fy
then hit the return key
It will run the repair disk for you.
You will know it's done when you see something like "your mac HD appears OK"
If you see anything but your HD is OK (like it was repaired sucessfully), then run the script again, until you see the words "your mac HD appears OK"
To get your computer back to normal.......type the following:
reboot
then hit the return key
This article -
http://support.apple.com/kb/TS1417 outlines the above steps in the section entitled