Cannot connect to Secured WirelessNetwork

Hi,
Some days back I have installed Windows 7 on my computer. Before that I had Windows XP on it. After installing Windows 7, I made sure everything, including my wireless network works fine with it. But after some days I found that my computer was not able to connect to my router. It is able to connect to all the other unsecured networks and to say I am a good time user of the computer, but not too technically sound in troubleshooting it.
So could anyone provide me a solution please?
