Mixed Speed Network problems?

I am running Windows Server 2003 at home, and had a gigabit lan connection to my internal network. Plugged into a 4 port switch, then into my router sharing the DSL internet connection we have.

The gigabit card has been working fine for a few months now. The system also has a built in 10/100 NIC.

This weekend I decided to change things up a bit, and connect my DSL modem directly to the server via the built in NIC.

Once I did this something odd happened.

Now my gigabit NICs speed has changed to 100m instead of 1000. I have triple check all my settings, and everything is the same on the gigabit NIC.

How can I fix this?

I was unaware of anything that would cause this, I expected the 2 devices to function independent to one another, but it seems that my built in NIC is somehow dictating what the overall speed of the entire network can be all of a sudden.

I disabled the built in NIC and removed the DSL connection, and it has not changed back to 1000 again either.

Any help would be greatly appreciated.