It can be many things:
1. Firewall with wrong settings?
2. Faulty configured QOS?
3. Another user on your local LAN is downloading?
4. Driver problem?
5. Browser problem?
So what I suggest is try another browser (doesn't matter which one). Open the browser and go to youtube search for some long video (try trance music, they are often very long). Now turn of your firewall completly. and let it play. If it don't comeback the firewall or the browser is the problem.
You can reinstall the driver:
http://www.tomshardware.co.uk/answers/id-2130169/wifi-connection-problem.html
(scroll a little down)
If this isn't the problem. Then come back and we will help you further.
hope this helps