Ta.... this is (obvously) going to be in English, if your router is in Spanish I'm afraid you'll have to translate :)
First click the link below
http://192.168.251.1
this should brong up the login prompt for your router, enter the username "sweex" and the password "mysweex" (these are the same regardless of the router language) and press enter...
Once the routers admin pages have loaded click on the link that says advanced and then on wireless and now click firstly on "access control" and if you see anything that says something along the lines of mac address filtering disable it and try again, if there is nothing that looks like mac address filtering move on to next paragraph :)
If it's still not working, now click on the security link at the top and make sure that it is set as the following...
Encryption - WPA2 mixed
authentication type - Auto
skip to WPA authentication type and select Personal (pre shared key)
pre shared key format - set to passphrase
Now type a password for your network into the box below marked pre shared key (this can be anything you want, it will become the password you need to connect any wireless device..)
Now you can click on submit and try connecting the kindle with the passphrase you've just entered.
**note... if you have any other wireless devices you'll need to reconnect them with the new passphrase you've just setup**
Manual for this router is available here .
http://www.sweex.com/...s/MO251/handleidingen