My black ink button on my pixma mp495 printer is blinking. Why?

Actually if the printer didnot work with the above answer which are written.you should do the following;1-take the catridge out and if it is empty,you can inject 3cc of ink slowly on the sponge of the cateidge, and replace it again then restart the printer.2-if this doesnot work,take the catridge out n replace it several times each time tune the printer on and off.3-the final solution is that,take the whole catridges out n clean the sponges of them which put in the ground of the printer ,then replace then again. Hope these work.

If the printer says the cartridges are empty, and will not let you print, just hold down the stop/reset button on the printer. That should clear the error.
Canon MP230 Override Empty Cartridge Message

A B LED light denotes that the black ink cartridge is running low.
A C LED light denotes that the colour ink cartridge is running low.
If the alarm light is on (lightning bolt in a triangle) it should be accompanied by an error code.
Canon MP495 - Error Codes If the printer displays an error message, the following information should help to diagnose the problem.
The led screen on the printer will flash a letter E and will then be followed by two numbers:
Error Description More Info Error E02 The machine is out of paper or will not feed. Error E03 Paper jam or output tray is closed. More Info Error E04 The Cartridge cannot be recognised. More Info Error E05 The Cartridge cannot be recognised. More Info Error E07 Cartridge is not installed in the correct position. More Info Error E08 Ink absorber is almost full. More Info Error E13 The remaining ink level cannot be detected. More Info Error E14 The Cartridge cannot be recognised. More Info Error E15 The Cartridge cannot be recognised. More Info Error E16 The ink has run out. More Info Error P02 Carriage encoder error. More Info Error P03 Line feed error. More Info Error P07 The waste ink absorber is full. More Info Error P08 Print head fault. More Info Error P10 Print head fault. More Info Error 5100 Carriage Encoder error. More Info Error 5200 Print head fault. More Info Error 6000 Line feed error. More Info Error B200 Print head fault. More Info Error 5B00 The waste ink absorber is full.