Why is my iMac clicking and having difficulty starting up?

In the past 2 weeks, my iMac has been making odd clicking noises when starting up and when waking from sleep. The motor drones to start up (accompanied by the clicking), will fail, and it will try starting again. It usually requires restart when I'm coming back from sleep. During start up, a folder icon with a question mark will flash. I have to restart around 10 times until the computer starts up normally (still with some clicking).

During use, the computer functions normally, although in the past day my computer will freeze my clicking power on my mouse. That is to say, my mouse can move around the screen, but clicking does nothing. This lasts about 2 minutes, and then my mouse works fine. Don't know if the problem is related.

Disk utility is not allowing me the option of "Repair Disk." When I verify disk with disk utility it reads:

Verifying volume “Macintosh HD”
Checking HFS Plus volume.
Checking Extents Overflow file.
Checking Catalog file.
Checking multi-linked files.
Checking Catalog hierarchy.
Checking Extended Attributes file.
Checking volume bitmap.
Volume Bit Map needs minor repair
Checking volume information.
Invalid volume free block count
(It should be 10795540 instead of 10795539)
The volume Macintosh HD needs to be repaired.

Error: The underlying task reported failure on exit


1 HFS volume checked
Volume needs repair

Can anyone help?