Coupons don't work

I'm working on a clean install of OC 1.5.2.1, and I've tried to create multiple coupons, none of which seem to be applied to the total. I enter the coupon number and click "Apply Coupon". The page refreshes but no discount is visible. No errors are displayed either. When the time comes to pay the amount given as the total is the full amount.

Would really appreciate some help with this, it's driving me insane.

At least give information about your Coupon setting.
You can check about the coupon date, minimum total for the coupon usage, limit of uses per customer / coupon, does coupon for all category or certain category.. etc

Hi Qahar, thanks for the reply

Coupon is as follows : The coupon is only usable by users who are logged in, only usable for items in a single category, coupon can be used 4 times by each customer. Coupon applies a 100% discount on items in the cart, so that customers only pay shipping.

It's been set up so that people can order samples 4 times for as close to free as possible.

Now the question is, when you apply coupon does your product is from "certain" category?
Since there is no error, I suggest you to try make a coupon for all product, without minimim total just test.

Hi how would I set up that a coupon cannot be used in conjunction with any specials, only full priced products.