Few things to check:

• Make sure you have a YN-622C directly on the hotshoe to act as transmitter. The PC port on the YN-622Cs is output-only--you cannot hook it up to the camera's PC port and have it act as a transmitter.

• Make sure all your batteries are in good health and fully charged. Bad or weak batteries in the flashes, camera, or triggers can make debugging what's going on harder.

• Make sure your triggers are on the same channel.

• Make sure you're in M mode, not TTL--the Novotron is a manual-only light and will not understand TTL, HSS, etc. You also will not be able to control it through the camera menu or the 622 triggers to do anything other than fire in sync with the camera shutter.

• Use the test button on the transmitter to see if the receiver fires the flash and/or lights up. If the triggers communicate, then it could be the camera-to-transmitter connection isn't good (so, if test button works, test the shutter button). And if the light isn't firing, but the triggers are communicating, then it's the trigger-to-the-flash sync connection.

• If the triggers simply aren't communicating, and you know they've got good batteries, and are on the same channel, then consider doing a factory reset.

Refer to the TOYUG (The Other YN-622C User Guide) for more details.

As an aside, make sure that what you think is the sync connector is the sync connector. Some of my googling mentions some Novatron lights use a HH (household) sync connection, not PC or 3.5mm miniplug, so if the M500 is one of these, you'd need a PC-to-HH cable to hook up a YN-622C to it.

Alternatively, the Novotron M500 also has a "dumb" optical slave on it, so you don't have to use radio triggers to pop it remotely. You would, however, need a flash on the 5DMkII (probably with the flash in M mode to avoid preflashes) to trigger it, since the 5DMkII doesn't have a pop-up flash.