Can't connect remotely to Windows Server 2008 R2

I have a new Dell R710 server running Windows Server 2008 R2. I one of it's 4 nic's set up and the rest are not being used. I have successfully given it an ip address, network mask, and dns servers. I can ping and resolve this machine from anywhere else in the network. However, when I try to connect to it via RDP it does several things:

1) it might just outright refuse me with the message, "This computer can't connect to the remote computer. Try connecting again." 2) it might connect me and let me chose the account I would like to log on as... but when you select an account then you receive the same message as in #1 3) it might actually allow you to connect but only for about 1 minute and then you receive the same message and it closes your session.

I have configured the firewall service to allow for RDP over the domain network connection. This didn't have any noticible effect. I have now disabled the firewall for all 3 networks and have even stopped the Windows Firewall service. I am still having the same issue.

I am new to Server 2008 R2 and things are very different. Please give me any advice you can on how to resolve this issue and/or any other gotchas that are sure to come my way. The 2003 -> 2008 learning curve seems steep.

Thanks

Update #1: I appear to be getting disconnected even when accessing network resources (file share) from the server in question. This is a Dell R710 which has 4 nics. I have only one connected and configured. I would think that these connections need not all be set up but perhaps I'm wrong?

Update #2: The same thing happens when I navigate to the default administrative share on the R710 server. About 50% of the time when I navigate from one directory to another I get the same message as stated in a below comment, "The computer can't connect to the remote computer. Try connecting again. If the problem continues, contact the owner of the remote computer or your network administrator". If I continue to try the same directory eventually I get in. Is this some sort of intelligent firewall service?¿

Update #3: I downloaded the latest Broadcom Nexxtreme II drivers for 64bit win 2008. Windows is telling me that my drivers are up to date. I also just tested RDP from the 2008 server to my XP SP3 workstation and it works fine. I would think at this point that the nic is operating fine. I also have several file shares that can be accessed in both directions. I feel as though this must be a firewall issue but when I turn off all firewalls for testing the same symptoms occur. Anyone have any more suggestions?