Right click on the wireless icon in system tray,choose,view available networks,and make sure you are trying to connect to your network and not someone elses with a low signal. Also go to the router homepage and temporarily disable security and see if you can connect now.
swanny2 - if it is a new connection they are prone to dropping whilst it is being optimised by the ISP. Usually a reboot of the router will re-connect you. If you are happy with the answers you have had please tick as resolved. Thanks. Hope this helps