Have you tried these?
1. Right-click the wireless icon in the Notification Area > Status > General Tab > Properties at the bottom, scroll down to Internet Protocol (TCP/IP) and double-click it. In the General Tab put dots in ‘Obtain an IP address automatically’ and in ‘Obtain DNS server address automatically’. OK, etc. Now go to a Run window (Windows key+R), type netsh winsock reset (note the two spaces) and press Enter. Shut down the computer.
2. Switch off and unplug the computer/router/modem. Wait five minutes, plug it the router/modem and when the lights stabilise, start the computer.