The first generation Kindle was a US only device and didn't have WiFi access so I'm going to assume you have a Keyboard Kindle which is a 3rd Generation model. You can check to see exactly which model you have by clicking on "Identify Your Device" at the top of this page.
Have you tried buying a free ebook using the website on a different device to see if that book downloads to your Kindle?
Has your Kindle connected in the recent past? Have you tried restarting both your Kindle and your Router? Have you checked to see if your Kindle is using the latest software?
As your Kindle is quite old, even if it won't connect to WiFi, you can always add books using a computer.
The 1st Generation Kindle never worked outside the US as it used the Carrier Sprint only, it wasn't until the International version of the Kindle 2 came out that they switched to AT&T and worked worldwide. The Kindle 2nd Gen devices were also 3G only.