Get out the manual for your router.  Log on to the router's configuration utility (I can't explain exactly how to do this because you haven't said which router you have).  Once in the configuration utility, you should be able to find the key in the wireless security settings.

Steve

croppin
On some other Dell Talk post (in case you are unable to do the instructions above) I saw someone saying you can totally clear out the access point back to factory settings by pressing and holding in (about a minute?) a reset button and then maybe cutting the power, waiting, and starting over with the setup. I remember doing something like that on our campus two summers ago when we were installing the first batch of our wireless access points from Aeronet (Cisco)