Well you have to have that disk or there is another way but a bit more complicated.. If it is beyond your capabilities let me know:
Start up your computer in single-user mode to reach the command line.
1. Shut down your Mac if it is on.
2. Press the power button to start the computer.
3. Immediately press and hold the Command (Apple) key and the "s" key for single-user mode. (Command-S)
You have successfully entered single-user mode when you see white text appear on the screen, that is called the command line.
At the command-line prompt type: /sbin/fsck -fy
Press Return. fsck will go through five "phases" and then return information about your disk's use and fragmentation. Once it finishes, it'll display this message if no issue is found:
** The volume (name_of_volume) appears to be OK If fsck found issues and has altered, repaired, or fixed anything, it will display this message: ***** FILE SYSTEM WAS MODIFIED *****
Important: If this message appears, repeat the fsck command you typed in step 2 until fsck tells you that your volume appears to be OK (first-pass repairs may uncover additional issues, so this is a normal thing to do).
When fsck reports that your volume is OK, type reboot at the prompt and then press Return.
Your computer should start up normally and allow you to log in.