If your computer won't start up normally, you may need to use a disk repair utility to fix the issue. Mac OS X includes two utilities for this�Disk Utility and fsck. You can also use these even when your computer starts just fine but you want to check the disk for possible file system issues. For Mac OS X 10.4.3 or later, check out "About live verification in Mac OS X 10.4.3 or later," below. Note: If you're using Mac OS X 10.4 or later, you should use Disk Utility instead of fsck, whenever possible. In some situations, file system errors may prevent your computer from starting up. This can occur after an improper shutdown, forced restart, or power interruption. If your computer shows any of the following symptoms on startup, use a disk repair utility: Your computer partially starts but then displays a command line in a text-only environment. You may see the message, "file system dirty, run fsck." Below it, you'll see what's called a command-line prompt, indicated by a number sign (#), that allows you to type a command. If you see this, you'll need to run fsck from the command line (see "Use fsck," below). Your computer starts but either it won't reach the login screen, or it may reach the login screen but not load the Desktop after you log in. However, you can start up in single-user mode. If your computer exhibits either of the above issues, here are some things to try to get your computer back to starting up properly again. If you can't find the system discs that came with your computer, see "Use fsck," below.