Hi, I have a Canon PIXMA iP4000 InkJet Photo

Sounds like a main board problem.

Here is a procedure for entering into the service menu.....

<Service mode operation procedures>
1) With the printer power turned off, while pressing the Resume/Cancel button, press and hold the Power button. (DO NOT release the buttons. The LED lights in
green to indicate that a function is selectable.)
2) While holding the Power button, release the Resume/Cancel button. (DO NOT release the Power button.)
3) While holding the Power button, press the Resume/Cancel button 2 times, and then release both the Power and Resume/Cancel buttons. (Each time the
Resume/Cancel button is pressed, the LED lights alternately in orange and green, starting with orange.)
4) When the LED lights in green, press the Resume/Cancel button the specified number of time(s) according to the function listed in the table below.

I have a PDF of the service manual available for free. GOTO www.Equipmentcity.net, and email me for a copy.