Ok, sadly this will be a bit tedious;
Please try the following. If you have any questions, just let me know.
1) Restart your Mac and hold the COMMAND and S keys together as soon as you hear the the start up chime. When the screen goes black and you start seeing text appear on screen, let go of the keys.
2) After a short period of time you will land at a command prompt (:/root#). At the command-line prompt, type:
and press Return.
- - -
“fsck” is a file system checker. It will run through a battery of tests, looking at different aspects of your file system.
When it's done, it will normally produce one of two messages
a) "The volume (name of your hard drive) appears to be OK
If it states the above, then your drive is fine and you can simply type "reboot" at the prompt and press Return to restart your Mac and boot back to the Desktop.
b) If fsck found any errors, it may have tried to correct them and will display this message: --FILE SYSTEM WAS MODIFIED--
If this message appears, repeat the fsck command you typed at the beginning:
and Press Return.
Keep repeating this until it reports your drive is OK.
If by some reason you need to do the above more than 5 times, this indicates a more serious issue. If this is the case please let know the error messages reported.
However, assuming everything goes okay, type 'reboot' at the prompt and then press Return.
Once it has finished restarting you should be back at the desktop. Does the Mac perform any differently?