Please accept my apologies for posting in an old thread. I had the problem described within, and looked here for a solution, however the solution turned out to be different and thought i'd add it for future visitors.
I too couldn't load web pages in IE or Firefox, but refresh almost always fixed this.
The mention of unstable DNS clued me in, and I logged into my Router settings, and accessed a page with my ADSL information such as who I connect to, password, username ect.. and within there, I could find the DNS servers of my ISP.
I then went into Network Connections, from the windows Control Panel. Choosing the properties of my LAN/Ethernet connection (i have a wired network, others may have wireless/WLAN).
Under the General tab is a list of "services" that the connection uses.
I chose Internet Protocol (TCP/IP), and clicked Properties, and then the Advanced... button.
This dialog has a tab called DNS. I had my router as the only DNS server (that's been fine before), so I then added the DNS server IP addresses into this, OK'd everything, and have not had the problem since.