How are you login in to router?
It is strongly recommended by All router suppliers that you use a physically connected
cable to the Router via a Ethernet RJ45 cable for router setup.
Using a wireless connected computer for setup is Not recommended to access router
Set-up at any time.
And are you SAVING the changes in the router?
Try this and see if it helps
Disable IPv6 In Vista
Windows Vista contains both the familiar IPv4 stack and the new IPv6 stack.
IPv6, when it's rolled out across the Internet over the next few years, will bring an end to
the problem of running out of IP addresses and improve other aspects of TCP/IP
However you do not need IPv6 at present time disable IPv6 in Vista
Download the pdf file will tell you how to disable IPv6 in Vista