WARNING: Make sure you turn off both your computer and all external equipment before you connect or disconnect equipment. Exception: It's OK to connect and disconnect USB (Universal Serial Bus) devices while the computer is on.

Follow these steps first

1	Shut down your computer.
2	Make sure all external devices are properly connected and turned on.
3	Do the following:
	• Make sure connectors are plugged in all the way. • Make sure thumbscrews are secure. • Make sure terminators are secure and their clips are fastened. • Remove devices (especially SCSI devices) that you do not use. • Remove SCSI-1 devices if you are also using SCSI-2 devices. (Older disks, usually under 200 MB in size, can cause problems when they are connected to a SCSI bus to which SCSI-2 devices are also connected.)
4	Restart your computer.
5	Make sure you've installed the necessary software to use each device.
	To run USB and other devices, you need to have software programs called "drivers" installed on your computer. Some software drivers are already installed. With other devices, you may need to install the drivers. For more information, see the documentation that came with your device. After installing the software, unplug the device and plug it back in.

If you're still experiencing problems

If you've followed the steps above and you're still experiencing problems, try to determine which piece of external equipment might be causing the problem.

1	Shut down your computer again.
2	Turn off and disconnect all external equipment (except your monitor and keyboard).
3	Restart the computer.
4	Reconnect each external device one by one. Start up your computer after connecting each device until the problem recurs.
5	When you determine which piece of equipment is causing the problem, refer to the documentation that came with the equipment, as well as the information on connecting equipment that came with your computer.

If you have a printer connected to your computer's SCSI port:
Make sure your printer is connected properly. Most printers connect to the printer port, not the SCSI port. Check the documentation that came with your printer for information on how to connect it properly.

If you are connected to an Ethernet network:
Your computer may not start up due to heavy network traffic. Disconnect the Ethernet cable, then start up again. Reconnect the Ethernet cable after the computer starts up. (It's OK to connect and disconnect an Ethernet cable while your computer is on.) Check to make sure Ethernet is still selected in the AppleTalk control panel.

If you suspect a keyboard or mouse problem:
Shut down your computer. Clean your mouse as described in your computer's manual or onscreen help. Borrow a Macintosh keyboard or mouse of the same type from another computer and connect it to yours. If that solves the problem, you may need to repair your keyboard or mouse. Consult an Apple-authorized service provider.

For more information

You can find more information about connecting external equipment in AppleCare Knowledge Base at
kbase.info.apple.com

Related topic

If your computer crashes, freezes, or won't start up