Since the issue is the reverting to a invalid dns server ip the usual reason for this is a malware or virus infection. This does assume you have not misconfigured your dhcp server to give the wrong dns record.
You would want to update and run your malware checker or antivirus software.
You may also want to consider going to a system restore point to before this began. This will undo any registry changes the malware/virus may have added.
Here's a little more detail in setting the dns servers vs the autoassigned dns server. You can use your ISP's dns servers or if in the US you can use Google's at 18.104.22.168 and 22.214.171.124
Start by going here:
Network and Internet
Right mouse click on the wifi or lan icon and go to properties
Double click on ipv4
Select "use the following dns server addresses"
put in the ipv4 ip addresses and click OK
For ivp6 you want to do the same as ipv4 but use these addresses instead since they are the ipv6 ips for Google in this case
2001:4860:4860::8888 and/or 2001:4860:4860::8844
and again say OK.
You don't need to reboot if using Win7 or 8
Let us know how it works out.