Strong Signal Not Internet


I have an iBook - it's about 3 years old. i use an airport card. Everything was fine until ... I have still a strong signal on my airport status window but when i want to connect to the internet - there is nothing. What is going on? Please help. I have not changed any of my settings or anything.
This happens to me every now and then, and the reason has always been that my base station has crashed. The middle light is on, but the other two are either off on constantly on. Pulling out the power cord and putting it back in after a couple of seconds usually does the trick.
How is your network configured? Any routers? Did you restart your ibook? If your answer is yes to the two previous questions follow what elander told you.
However, if the restart of your router didn't work, you should enter your routers web-interface and check your WAN settings and if your WAN is connected.
And welcome to the forum.