My HP PSC 1401 printer always prints the test page

Take the test page ( also called : alighnment page ) that always prints when you switch on the printer and place it face down in the scanner.

Then press the scan button on the printer itself.
(this is the button at the bottom of all the buttons on the printer/scanner.)

Make sure that the printer scans the test page.
( sometimes you press the butoon and it doesn't scan )
( it makes a scanning noise when scanning succesfully )

An addition to super cutes answer, it won't happen again till your replace the cartridge again.