If you are getting no color out of your toner cartridge(s), but the cartridges are actually going through the motion of printing and the printer is accepting them, the possibilities are;
 
1.       Look at the developing roller. Is there toner on the roller?  You should see toner on the roller.

2.       The developer roller may not be turning. Place a small dot on the roller with a marker pen in the region showed by the #1 in the attached pic (in this region, there is no toner). Insert the cartridge into the printer & let the printer come to Ready (this should turn the cartridge roller as the machine warms up). Pull the cartridge out & look at the roller. Is the dot in the same position (indicating the roller is not turning) or has the dot  moved (roller is turning).

a.       If the roller has not turned, then you may be missing a gear. Check to see all gears are in place.

b.      If the roller has turned & there is toner on the roller, then there may be an electrical connection issue. There is only one electrical connection to the cartridge (see attached pic). The copper colored contact may be bent and not making contact with the drum unit.