Airport trouble: could not connect to wireless network: timeout

Hi there, maybe someone can help me...

I´ve massive trouble with connecting my wireless network via Airport. I´ve a MacBook (2008) with Lion. My connection was working till last week. I´vnt changed any setting or something... I was working like every day. From one secound to another the connection to my network was broken. When I try to connect to my network my Mac gives a trouble message: "timeout". I allready checked my router config (192.168.0.1 as admin) and everything is fine. No MAC Filter! Everything is set like it´s written in the apple manual. I allready restarted my router. Plugged it completly off. Not working. I was so desperated that I installed my system (Lion) new 2 days ago. The connection problem is still there! I don´t now where the problem is! I can connect with my MacBook to any other wireless network and via ethernet. The router is working fine because I can connect with my other laptop to it (by the way with 2 iphone as well). Do anyone no this problem? I don´t know what to do now. Who can help me??? You would make my day!