The signals won't flash (stock type flasher) unless you have about 13 volts or more. This means they won't flash when the engine is off. Is your engine on or off?
Even if your engine is running, but the charging system is not working (meaning you only have approx. 12.4 volts), they won't flash.
Any item in the path, that supplies the voltage to the flasher unit, can have a higher that normal resistance and cause voltage drops. The main fuse, ignition switch or signals fuse can cause this to happen. Use a VOM to measure voltage at the flasher unit.