Adwords re-targeting shows ads to people who have been to your site and then go to other sites around the web. If you are not getting imp somethings to check are
Check if your list is gaining users - You have to have a minimum of 100 users to start to see impr
Check your ads are approved and not on hold
Check you have popular ad formats ie 300 x 250 or text ads
Check your bid price it may be too low
If you still have issue give google a call