I used to use a fixed IP and fixed DNS server in TCP/IP (v4) properties of my wireless network connection. I recently got a new router, started using DHCP and changed TCp/IP properties to obtain addresses automatically. This works fine. EXCEPT that every few hours, apparently without any external trigger, I find that I can no longer get email or internet access, and on investigating the wireless connection's TCP/IP properties, I find that it has reverted to "Use the following DNS server addresses", and has put the address of my old router in there. That address is no longer in use on the network, hence no Internet access. Changing it back to "Obtain DNS server address automatically" fixes the problem instantly ... until the next time. Any ideas what's going on? I guess I could fix it just by hard-coding a valid DNS server address (e.g. the address of the router) but I'd rather find a proper fix. Using Win 7 Home Premium x64 on a Sony Vaio.

This could be something flaky with the driver. As a simple test, I would go into device manager, unistall the adapter, then rescan and let OS find the hardware once again. You should take the opportunity to provide the latest driver downloaded from the vendor's website. Visit: anITKB.com, an IT Knowledge Base.