If you are out of colored ink:
Hold down the resume/cancel button. The resume/cancel button is the smaller button below the power button, on the right side of the front of the printer. Press for 10 seconds. You can now print in black ink.
If the printer is completely out of ink, you will see the alarm lamp, to the left of the resume/cancel button, flash orange four times to indicate the ink supply is low. You'll need to replace the ink cartridges.
For more information, please refer to this device's troubleshooting page.