The turn signal or hazard warning do not flash. All bulbs check o.k.
blinker/ flasher do not work on 2004 Chevrolet Impala
If the bulbs and fuses all check ok then I would suspect a faulty hazard switch. The hazard switch also controls the "flashing" of both the turn signals and the hazard lights. Try turning on and off the hazard switch a few times to see if you can get the lights to start working again.
Russ is right its probably the hazard switch its available at http://www.parts.com/ put in your year make and model then put hazard in the search box about $50 plus shipping