If a power cycle does not work then it could be a incorrectly entered WEP key, if you go to the network connections section from control panel, then right click on your wireless network connection and select properties. Go to your saved wireless networks and remove it.
This will allow you to search for and add your wireless network again, enter the correct WEP key, if this does not work try resetting your wireless key on the router page (you will then need to re-enter on your other devices such as PS3 etc)
If all else fails you could try changing the wireless channel.
Does your wireless card connect to other wireless networks? Are you within range of your Router, if you are a long way from the router signal strenght could be a issue?