Internet from datacard doesn't work when LAN is enabled

[Ultra_Bloodshed]

I am unsure if this is a hardware problem or software. I am assuming it's a software based problem and so I am posting it here.

I have a Huawei E303C datacard with a Docomo3G connection. When I insert the datacard to the system and connect successfully, internet works fine and I can browse without problems. I have no enabled LAN connection during this time.

So now, I insert the LAN cable to my ethernet port to connect to my another system in another room. LAN is successfully connected and I can access the other system. But now, internet is no longer working! The dialer shows that I am connected to the internet, but web pages don't open. If I disable the LAN again, internet magically comes back. Keep in mind I am not disconnecting and reconnecting with the dialer at any time. Even if I do that, there is no change.

But the strange thing is that suppose I am on a google chat when net is working, if I enable the LAN connection, internet goes kaput, but the chat which was going on still works. But if I try to open another chat window with another person, it won't work again.

Any help will be usefull here, fellas. Am running Windows 7 (64-bit).
- Datacard connection in "Network Connections" - Mobile Broadband Connection
- LAN connection in "Network Connections" - Local Area Connection 2

 

[kisame]

In the Network Connections page, click Advanced->Advanced Options(or it may be Tools->Advanced Options) from the menu.There, you can see the priority of your connections.
Change it according to our needs.

 

[Ultra_Bloodshed]

I have already done that. "Mobile Broadband Connection" which has the internet, is on the top.

 

[Ascendant001]

its not the position which matters.in the network sharing center---adapter settings right click the docomo connection & select "set as default connection".