I have been battling this problem for over a month now.
I lose connection to the internet at random times. Eventually, I figured out that under TCP/IPv4 Properties, "Obtain DNS server address automatically" is being changed to "User the following DNS server addresses", and then an IP address would be specified for "Preferred DNS server". When I undo this change and choose "obtain DNS server address automatically", I regain my internet connection.
I tried checking these settings at random times when there is no problem with my internet connection. Most of the time the setting is unchanged. But sometimes a Preferred DNS server is specified. It feels like at those times, my internet speed is slower than usual, but I can't be sure.
I have Windows 7. I tried scanning my computer with Microsoft Security Essentials, but it didn't find anything.
When I used HijackThis. I attempted to fix some entries that didn't look right. However, when I scan my pc using HijackThis again, it displays all of the entries that it said it fixed the last time. In addition, when I tried clicking "analyze this" in HijackThis, I received an error message that I wasn't connected to the internet (even though I could load websites).
You can imagine how grateful I would be if I were to receive any help with this nightmare.
Thank you for considering this problem and for reading my message.