Server randomly stops services

I have Windows 2003 with two network interface cards. This server runs websites and has terminal services enabled. Websites and terminal services randomly stop working and come back on their own within about 10 minutes. I don’t think it is a firewall issue. There is nothing about it in the event logs.
I think it is something to do with the network cards. What is the best way to configure two network cards? Their speed is currently set to “Auto-negotiate best speed”
NICs are Intel Pro 1000 CT & Intel Pro 1000 MT
I appreciate any advice.Thank you