If you purchased a new retail adapter from a dealer, the limited lifetime hardware warranty from Intel applies. See http://www.intel.com/support/network/sb/cs-009721.htm for details. The bottom of this page has links to an RMA form or contact information for Intel Customer Support. The retail boards have a product code on one of the labels that says EXPI9404PTL or EXPI9404PTLBLK.
If you bought the adapter second-hand or if you have an OEM version of the adapter, you would have to check with the place where you bought the adapter to find out their policy for warranty, returns, or other support.
I hope this helps.