Clear all the cache and temporary files from your web browsers
Make sure you haven't got a proxy set
Try and flush the DNS
Windows Key + R Key>CMD> ipconfig /flushdns
Release and Renew your IP Address settings
Windows Key + R Key>CMD> ipconfig /release
Windows Key + R Key>CMD> ipconfig /renew
Try some ping tests
Windows Key + R Key>CMD> ping 192.168.0.1 (assuming that is your router address)
Then
Windows Key + R Key>CMD> ping
www.google,comhttp://www.google.com (you can use any website here)
you could use the test ping
www.google,com -t
this will do a none stop test, rather than just testing 4 times.
this will help you to see if your computer has an issues with connecting to the router, and then to a website.
This test cuts out the web browser, so if everything comes back ok from the ping tests you know it is not a network connection issue and can concentrate on you OS and one of the browsers, and if it shows slowness in the ping tests you can then concentrate on the network side of things.