If your Mac has been in use for some time, or if something happens, then using your Mac's disk utility for first-aid self-test and repair is a very necessary thing, and here's a new friend about how to self-test and fix disks on your Mac.
Open the application first-use tools-disk Utility
After opening the disk utility, select your disk on the left (commonly called Macintosh HD) and select [First Aid] on the Right tab.
Click "Verify Disk" at the bottom right to start the self-test
This time you will be prompted to self-test the computer will be slow, while verifying that the disk starts, the dialog box will appear a lot of detection information, report disk detection results. If there is a problem with your disk, a red letter prompt appears. Of course, the general user's disk is normal, after detection will prompt you all normal.
If there is a red word error, you can try to directly select the "Repair Disk" option below the interface, but if the system directly prompts you to start the disk "corrupted" and other similar information, it is not easy to repair, need to restart the system.
After 10.7Lion, the system can be repaired by recovery HD, but it is recommended to use a time machine backup before the repair is better:
Restart your Mac hold +r until you see the apple and let go.
Enter recovery HD, in the Mac OS x utility, select "Disk Utility" here
Select the disk you just have problems with and select "Repair Disk" in first aid
In general, the normal restart problem can be solved after this repair. For older systems such as the 10.6, you can choose to use the CD-ROM of the purchased machine to find the disk utility from the CD and repair it.