Where did you get the motors from? Are they the rated at the same speed? And do they spin at all? I have bought those types of motors from ebay before and sometimes they give me a completely different speed that i have asked for. Sometimes I have also been given random dodgy motors that dont work properly either.

Also how have you connected your motors together? are they in series or parallel? This last question is just for interest as i doubt that will be causing your problem