Default gateway changes after reboot

I am having problems with my internet connection. I am running a pc behind a router with DHCP enabled.

Often when I restart the computer the computers internal IP is also set as the default gateway.

My router is 192.168.1.1

My computer gets automatically IP 192.168.1.4
and then gets Default gateway of 192.168.1.4

Then I have to manually set the default gateway to 192.168.1.1 for it to work. But next time I use the computer the gateway has changed again and I have to change back.

What to do? I have the latest network drivers for my nvidia mobo and running windows 7.

The name of the network I am connected to also changes a lot.

1. Yes, upgraded two days ago.
2. Filled in most of them now.
3. Avast Antivirus and windows firewall.
4. Wired network (wireless turned off) on a Netgear router.

Thanks. It did work.

Not sure way I had to do it. Should have worked with original settings. But what the heck ! :)

Plz uninstall previous lan card software from ur PC,and reboot the PC and install again lan card software...I hope ur problem will be solved....:)