Welcome to SF,
Please try these resommendations:
Are you using any 3rd party utility manager to wireless connect? If you do, you have to disable the WLAN Auto Config
for Vista/7 from Control Panel's Services. Click on Start and type services.exe, press enter locate WLAN Auto Config and Disable. Otherwise, if no wireless utility is installed, WLAN Auto config needs to be enabled.
Make sure that DHCP and Obtain DNS server address automatically is enabled from both LAN and Wireless connection. Here's How
Disable the problematic Wireless Network Adapter's power saving mode from Device Manager, locate the Network Adapter=> Properties=> Power Management Tab, in here you may disable any Power Save mode options by unchecking them off.